Copyright 2000 Michael Abraham Shulman.

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MMM Mode
********

MMM Mode is a minor mode for Emacs which allows Multiple Major Modes to coexist in a single buffer.

Overview of MMM Mode
********************

MMM Mode is a minor mode for Emacs which allows Multiple Major Modes to coexist in a single buffer. The name is an abbreviation of `Multiple Major Modes' (The name is derived from mmm.el for XEmacs by Gongquan Chen <chen@posc.org>, from which MMM Mode was adapted.). A major mode is a customization of Emacs for editing a certain type of text, such as code for a specific programming language. See Major Modes (The Emacs Manual), for details.

MMM Mode is a general extension to Emacs which is useful whenever one file contains text in two or more programming languages, or that should be in two or more different modes.  For example:

  * CGI scripts written in any language, from Perl to PL/SQL, may want to output verbatim HTML, and the writer of such scripts may want to use Emacs' html-mode or sgml-mode to edit this HTML code, while remaining in the appropriate programming language mode for the rest of the file.  See Here-documents, for example.

  * There are now many ``content delivery systems'' which turn the CGI script idea around and simply add extra commands to an HTML file, often in some programming language, which are interpreted on the server.  See Mason, see Embperl, see ePerl, see JSP.

  * HTML itself can also contain embedded languages such as Javascript and CSS styles, for which Emacs has different major modes. See Javascript, and see Embedded CSS, for example.

  * The idea of ``literate programming'' requires the same file to contain documentation (written as text, html, latex, etc.) and code (in an appropriate programming language).  See Noweb, for example.

  * Emacs allows files of any type to contain `local variables', which can include Emacs Lisp code to be evaluated. See File Variables (The Emacs Manual). It may be easier to edit this code in Emacs Lisp mode than in whatever mode is used for the rest of the file. See File Variables.

  * There are many more possible uses for MMM Mode.  RPM spec files can contain shell scripts (see RPM).  Email or newsgroup messages may contain sample code.  And so on.  We encourage you to experiment.

Basic Concepts
==============

The way MMM Mode works is as follows. Each buffer has a dominant or default major mode, which is chosen as major modes normally are: the user can set it interactively, or it can be chosen automatically with `auto-mode-alist' (see Choosing Modes (The Emacs Manual)). Within the file, MMM Mode creates submode regions within which other major modes are in effect. While the point is in a submode region, the following changes occur:

 1. The local keymap is that of the submode. This means the key bindings for the submode are available, while those of the dominant mode are not.

 2. The mode line (see Mode Line (The Emacs Manual)) changes to show which submode region is active. This can be configured; see Mode Line.

 3. The major mode menu, both on the menu bar and the mouse popup, are that of the submode.

 4. Some local variables of the submode shadow those of the default mode (see Local Variables). For the user, this serves to help make Emacs behave as if the submode were the major mode.

 5. The syntax table and indentation are those of the submode.

 6. Font-lock (see Font Lock (The Emacs Manual)) fontifies correctly for the submode.

 7. The submode regions are highlighted by a background color; see Region Coloring.

The submode regions are represented internally by Emacs Lisp objects known as overlays. Some of the above are implemented by overlay properties, and others are updated by an MMM Mode function in `post-command-hook'. You don't need to know this to use MMM Mode, but it may make any error messages you come across more understandable. See Overlays (The GNU Emacs Lisp Reference Manual), for more information on overlays.

Because overlays are not saved with a file, every time a file is opened, they must be created.  Creating submode regions is occasionally referred to as mmm-ification.  (I've never had occasion to pronounce this, but if I did I would probably say `mummification'. Like what they did in ancient Egypt.)  You can mmm-ify a buffer interactively, but most often MMM Mode will find and create submode regions automatically based on a buffer's file extension, dominant mode, or local variables.

Installing MMM Mode
===================

MMM Mode has a standard installation process.  See the file INSTALL for generic information on this process.  To summarize, unpack the archive, cd to the created MMM Mode directory, type ./configure, then make, then make install.  If all goes correctly, this will compile the MMM Mode elisp files, install them in your local site-lisp directory, and install the MMM Mode info file mmm.info in your local info directory.

Now you need to configure your Emacs initialization file (usually ~/.emacs) to use MMM Mode.  First, Emacs has to know where to find MMM Mode.  In other words, the MMM Mode directory has to be in load-path.  This can be done in the parent directory's subdirs.el file, or in the init file with a line such as:

     (add-to-list 'load-path "/path/to/site-lisp/mmm/")

Once load-path is configured, MMM Mode must be loaded.  You can load all of MMM Mode with the line

     (require 'mmm-mode)

but if you use MMM Mode only rarely, it may not be desirable to load all of it at the beginning of every editing session.  You can load just enough of MMM Mode so it will turn itself on when necessary and load the rest of itself, by using instead the line

     (require 'mmm-auto)

in your initialization file.

One more thing you may want to do right now is to set the variable mmm-global-mode.  If this variable is nil (the default), MMM Mode will never turn itself on.  If it is t, MMM Mode will turn itself on in every buffer.  Probably the most useful value for it, however, is the symbol maybe (actually, anything that is not nil and not t), which causes MMM Mode to turn itself on in precisely those buffers where it would be useful.  You can do this with a line such as:

     (setq mmm-global-mode 'maybe)

in your initialization file.  See Global Mode, for more detailed information.

Getting Started Quickly
=======================

Perhaps the simplest way to create submode regions is to do it interactively by specifying a region. First you must turn MMM Mode on---say, with M-x mmm-mode---then place point and mark around the area you want to make into a submode region, type C-c % C-r, and enter the desired major mode. See Interactive, for more details.

A better way to add submode regions is by using submode classes, which store a lot of useful information for MMM Mode about how to add and manipulate the regions created.  See Submode Classes, for more details.  There are several sample submode classes that come with MMM Mode, which are documented later in this manual.  Look through these and determine if one of them fits your needs.  If so, I suggest reading the comments on that mode.  Then come back here to find out to use it.

To apply a submode class to a buffer interactively, turn MMM Mode on as above, then type C-c % C-c and enter the name of the class. Submode regions should be added automatically, if there are any regions in the buffer appropriate to the submode class.

If you want a given file to always use a given submode class, you can express this in a file variable: add a line containing the string -*- mmm-classes: CLASS -*- at the top of the file. See File Variables (The Emacs Manual), for more information and other methods. Now whenever MMM Mode is turned on in that file, it will be mmm-ified according to CLASS. If mmm-global-mode is non-nil, then MMM Mode will turn itself on whenever a file with a mmm-classes local variable is opened. See Global Mode, for more information.

If you want a submode class to apply to all files in a certain major mode or with a certain extension, add a line such as this to your initialization file:

     (mmm-add-mode-ext-class MODE EXTENSION CLASS)

After this call, any file opened whose name matches the regular expression EXTENSION and whose default mode is MODE will be automatically mmm-ified according to CLASS (assuming mmm-global-mode is non-nil). If one of EXTENSION or MODE is nil, a file need only satisfy the other one to be mmm-ified.

You can now read the rest of this manual to learn more about how MMM Mode works and how to configure it to your preferences.  If none of the supplied submode classes fit your needs, then you can try to write your own.  See Writing Classes, for more information.

MMM Mode Basics
***************

This chapter explains the most important parts of how to use MMM Mode.

The MMM Minor Mode
==================

An Emacs minor mode is an optional feature which can be turned on or off in a given buffer, independently of the major mode. See Minor Modes (The Emacs Manual). MMM Mode is implemented as a minor mode which manages the submode regions. This minor mode must be turned on in a buffer for submode regions to be effective. When activated, the MMM Minor mode is denoted by MMM in the mode line (see Mode Line).

Enabling MMM Mode
-----------------

If mmm-global-mode is non-nil (see Global Mode), then the MMM minor mode will be turned on automatically whenever a file with associated submode classes is opened (see Selecting Classes). It is also turned on by interactive mmm-ification (see Interactive), although the interactive commands do not have key bindings when it is not on and must be invoked via M-x. You can also turn it on (or off) manually with M-x mmm-mode, in which case it applies all submode classes associated with the buffer. Turning MMM Mode off automatically removes all submode regions from the buffer.

 -- Command: mmm-mode ARG
     Toggle the state of MMM Mode in the current buffer. If ARG is supplied, turn MMM Mode on if and only if ARG is positive.

 -- Function: mmm-mode-on
     Turn MMM Mode on unconditionally in the current buffer.

 -- Function: mmm-mode-off
     Turn MMM Mode off unconditionally in the current buffer.

 -- Variable: mmm-mode
     This variable represents whether MMM Mode is on in the current buffer. Do not set this variable directly; use one of the above functions.

Key Bindings in MMM Mode
------------------------

When MMM Mode is on, it defines a number of key bindings. By default, these are bound after the prefix sequence C-c %. Minor mode keymaps are supposed to use C-c PUNCTUATION sequences, and I find this one to be a good mnemonic because % is used by Mason to denote special tags. This prefix key can be customized; Key Bindings.

There are two types of key bindings in MMM Mode: commands and insertions. Command bindings run MMM Mode interactive functions to do things like re-parse the buffer or end the current submode region, and are defined statically as normal Emacs key-bindings. Insertion bindings insert submode region skeletons with delimiters into the buffer, and are defined dynamically, according to which submode classes (see Submode Classes) are in effect, via a keymap default binding.

To distinguish between the two, MMM Mode uses distinct modifier keys for each. By default, command bindings use the control key (e.g. C-c % C-b re-parses the buffer), and insertion bindings do not (e.g. C-c % p, when the Mason class is in effect, inserts a <%perl>...</%perl> region). This makes the command bindings different from in previous versions, however, so the variable mmm-use-old-bindings is provided. If this variable is set to `t' before MMM Mode is loaded, the bindings will be reversed: insertion bindings will use the control key and command bindings will not.

Normally, Emacs gives help on a prefix command if you type C-h after that command (e.g. C-x C-h displays all key bindings starting with C-x). Because of how insertion bindings are implemented dynamically with a default binding, they do not show up when you hit C-c % C-h. For this reason, MMM Mode defines the command C-c % h which displays a list of all currently valid insertion key sequences. If you use the defaults for command and insertion bindings, the C-h and h should be mnemonic.

In the rest of this manual, I will assume you are using the defaults for the mode prefix (C-c %) and the command and insertion modifiers. You can customize them, however; Key Bindings.

Understanding Submode Classes
=============================

A submode class represents a ``type'' of submode region. It specifies how to find the regions, what their delimiters look like, what submode they should be, how to insert them, and how they behave in other ways. It is represented by a symbol, such as mason or eval-elisp.

For example, in the Mason set of classes, there is one class representing all <%...%> inline Perl regions, and one representing regions such as <%perl>...</%perl>, <%init>...</%init>, and so on. These are different to Mason, but to Emacs they are all just Perl sections, so they are covered by the same submode class.

But it would be tedious if whenever we wanted to use the Mason classes, we had to specify both of these. (Actually, this is a simplification: there are some half a dozen Mason submode classes.) So submode classes can also ``group'' others together, and we can refer to the mason class and mean all of them.

The way a submode class is used is to apply it to a buffer. This scans the buffer for regions which should be submode regions according to that class, and also remembers the class for later, so that new submode regions can be inserted and scanned for later.

How MMM Mode selects submode classes
====================================

Submode classes that apply to a buffer come from three sources: mode/extension-associated classes, file-local classes, and interactive MMM-ification (see Interactive). Whenever MMM Mode is turned on in a buffer (see MMM Minor Mode, and Global Mode), it inspects the value of two variables to determine which classes to automatically apply to the buffer. This covers the first two sources; the latter is covered in a later chapter.

File-Local Submode Classes
--------------------------

 -- Variable: mmm-classes
     This variable is always buffer-local when set. Its value should be either a single symbol or a list of symbols. Each symbol represents a submode class that is applied to the buffer.

mmm-classes is usually set in a file local variables list. See File Variables (The Emacs Manual). The easiest way to do this is for the first line of the file to contain the string -*- mmm-classes: CLASSES -*-, where CLASSES is the desired value of mmm-classes for the file in question. It can also be done with a local variables list at the end of the file.

Submode Classes Associated with Modes and Extensions
----------------------------------------------------

 -- User Option: mmm-mode-ext-classes-alist
     This global variable associates certain submode classes with major modes and/or file extensions. Its value is a list of elements of the form (MODE EXT CLASS). Any buffer whose major mode is MODE (a symbol) and whose file name matches EXT (a regular expression) will automatically have the submode class CLASS applied to it.

     If MODE is nil, then only EXT is considered to determine if a buffer fits the criteria, and vice versa. Thus if both MODE and EXT are nil, then CLASS is applied to all buffers in which MMM Mode is on. Note that EXT can be any regular expression, although its name indicates that it most often refers to the file extension.

     If CLASS is the symbol t, then no submode class is actually applied for this association. However, if mmm-global-mode is non-nil and non-t, MMM Mode will be turned on in matching buffers even if there are no actual submode classes being applied. See Global Mode.

 -- Function: mmm-add-mode-ext-class MODE EXT CLASS
     This function adds an element to mmm-mode-ext-classes-alist, associating the submode class CLASS with the major mode MODE and extension EXT.

     Older versions of MMM Mode required this function to be used to control the value of mmm-mode-ext-classes-alist, rather than setting it directly. In this version it is provided purely for convenience and backward compatibility.

Globally Applied Classes and the Universal Class
------------------------------------------------

In addition to file-local and mode-ext-associated submode classes, MMM Mode also allows you to specify that certain submode classes apply to all buffers in which MMM Mode is enabled.

 -- User Option: mmm-global-classes
     This variable's value should be a list of submode classes that apply to all buffers with MMM Mode on.  It can be overriden in a file local variables list, such as to disable global class for a specific file. Its default value is (universal).

The default global class is the ``universal class'', which is defined in the file mmm-univ.el (loaded automatically), and allows the author of text to specify that a certain section of it be in a specific major mode.  Thus, for example, when writing an email message that includes sample code, the author can allow readers of the message (who use emacs and MMM) to view the code in the appropriate major mode.  The syntax used is {%MODE%} ... {%/MODE%}, where MODE should be the name of the major mode, with or without the customary -mode suffix: for example, both cperl and cperl-mode are acceptable.

The universal class also defines an insertion key, /, which prompts for the submode to use.  See Insertion.  The universal class is most useful when mmm-global-mode is set to t; Global Mode.

Inserting new submode regions
=============================

So much for noticing submode regions already present when you open a file. When editing a file with MMM Mode on, you will often want to add a new submode region. MMM Mode provides several facilities to help you. The simplest is to just hit a few keys and have the region and its delimiters inserted for you.

Each submode class can define an association of keystrokes with ``skeletons'' to insert a submode region. If there are several submode classes enabled in a buffer, it is conceivable that the keys they use for insertion might conflict, but unlikely as most buffers will not use more than one or two submode classes groups.

As an example of how insertion works, consider the Mason classes. In a buffer with MMM Mode enabled and Mason associated, the key sequence C-c % p inserts the following perl section (the semicolon is to prevent CPerl Mode from getting confused---see Mason):

     <%perl>-<-;
     -!-
     ->-</%perl>

In this schematic representation, the string -!- represents the position of point (the cursor), -<- represents the beginning of the submode region, and ->- its end.

All insertion keys come after the MMM Mode prefix keys (by default C-c %; see Key Bindings) and are by default single characters such as p, %, and i. To avoid confusion, all the MMM Mode commands are bound by default to control characters (after the same prefix keys), such as C-b, C-% and C-r. This is a change from earlier versions of MMM Mode, and can be customized; see Key Bindings.

To find out what insertion keys are available, consult the documentation for the submode class you are using. If it is one of the classes supplied with MMM Mode, you can find it in this Info file.

Because insertion keys are implemented with a ``default binding'' for flexibility, they do not show up in the output of C-h m and cannot be found with C-h k. For this reason, MMM Mode supplies the command C-c % h (mmm-insertion-help to view the available insertion keys.

Re-Parsing Submode Regions
==========================

Describe mmm-parse-buffer, mmm-parse-region, mmm-parse-block, and mmm-clear-current-region.

Interactive MMM-ification Functions
===================================

There are several commands you can use to create submode regions interactively, rather than by applying a submode class to a buffer. These commands (in particular, mmm-ify-region), can be useful when editing a file or email message containing a snippet of code in some other language.  Also see Global Classes, for an alternate approach to the same problem.

C-c % C-r
     Creates a submode region between point and mark. Prompts for the submode to use, which must be a valid Emacs major mode name, such as emacs-lisp-mode or cperl-mode. Adds markers to the interactive history. (mmm-ify-region)

C-c % C-c
     Applies an already-defined submode class to the buffer, which it prompts for. Adds this class to the interactive history. (mmm-ify-by-class)

C-c % C-x
     Scans the buffer for submode regions (prompts for the submode) using front and back regular expressions that it also prompts for. Briefly, it starts at the beginning of the buffer and searches for the front regexp. If it finds a match, it searches for the back regexp. If it finds a match for that as well, it makes a submode region between the two matches and continues searching until no more matches are found. Adds the regexps to the interactive history. (mmm-ify-by-regexp)

These commands are also useful when designing a new submode class (see Submode Classes). Working with the regexps interactively can make it easier to debug and tune the class before starting to use it on automatic. All these commands also add to value of the following variable.

 -- Variable: mmm-interactive-history
     Stores a history of all interactive mmm-ification that has been performed in the current buffer. This way, for example, the re-parsing functions (see Re-parsing) will respect interactively added regions, and the insertion keys for classes that were added interactively are available.

If for any reason you want to ``wipe the slate clean'', this command should help you. By default, it has no key binding, so you must invoke it with M-x mmm-clear-history RET.

 -- Command: mmm-clear-history
     Clears all history of interactive mmm-ification in the current buffer. This command does not affect existing submode regions; to remove them, you may want to re-parse the buffer with C-c % C-b (mmm-parse-buffer).

MMM Global Mode
===============

When a file has associated submode classes (see Selecting Classes), you may want MMM Mode to turn itself on and parse that file for submode regions automatically whenever it is opened in an Emacs buffer. The value of the following variable controls when MMM Mode turns itself on automatically.

 -- User Option: mmm-global-mode
     Do not be misled by the fact that this variable's name ends in -mode: it is not a simple on/off switch. There are three possible (meanings of) values for it: t, nil, and anything else.

     When this variable is nil, MMM Mode is never enabled automatically. If it is enabled manually, such as by typing M-x mmm-mode, any submode classes associated with the buffer will still be used, however.

     When this variable is t, MMM Mode is enabled automatically in all buffers, including those not visiting files, except those whose major mode is an element of mmm-never-modes. The default value of this variable contains modes such as help-mode and dired-mode in which most users would never want MMM Mode, and in which MMM might cause problems.

     When this variable is neither nil nor t, MMM Mode is enabled automatically in all buffers that would have associated submode classes; i.e. only if there would be something for it to do. The value of mmm-never-modes is still respected, however. Note that this can include buffers not visiting files, if that buffer's major mode is present in mmm-mode-ext-classes-alist with a nil value for EXT (see Mode-Ext Classes). Submode class values of t in mmm-mode-ext-classes-alist cause MMM Mode to be enabled in matching buffers, but supply no submode classes to be applied.

The Major Mode Hook
-------------------

This section is intended for users who understand Emacs Lisp and want to know how MMM Global Mode is implemented, and perhaps use the same technique. In fact, MMM Mode exports a hook variable that you can use easily, without understanding any of the details---see below.

In order to enable itself in all buffers, however, MMM Mode has to hook itself into all major modes.  Global Font Lock Mode from the standard Emacs distribution (see Font Lock (The Emacs Manual)) has a similar problem, and solves it by adding a function to change-major-mode-hook, which is run by kill-all-local-variables, which is run in turn by all major mode functions at the beginning.  This function stores a list of which buffers need fontification.  It then adds a different function to post-command-hook, which checks if the current buffer needs fontification, and if so performs it.  MMM Global Mode uses the same technique.

In the interests of generality, and for your use, the function that MMM Mode runs in post-command-hook (mmm-run-major-mode-hook) is not specific to MMM Mode, but rather runs the hook variable mmm-major-mode-hook, which by default contains a function (mmm-mode-on-maybe) which possibly turns MMM Mode on, depending on the value of mmm-global-mode.  Thus, to run another function in all major modes, all you need to do is add it to this hook.  For example, the following line in an initialization file will turn on Auto Fill Mode (see Auto Fill (The Emacs Manual)) in all buffers:

     (add-hook 'mmm-major-mode-hook 'turn-on-auto-fill)

Customizing MMM Mode
********************

This chapter explains how to customize the appearance and functioning of MMM Mode however you want.

Customizing Region Coloring
===========================

By default, MMM Mode highlights all submode regions with a background color.  There are three levels of this decoration, controlled by the following variable:

 -- User Option: mmm-submode-decoration-level
     This variable controls the level of coloring of submode regions.  It should be one of the integers 0, 1, or 2, representing (respectively) none, low, and high coloring.

No coloring means exactly that.  Submode regions have the same background as the rest of the text.  This produces the minimal interference with font-lock coloration.  In particular, if you want to use background colors for font-lock, this may be a good idea, because the submode highlight, if present, overrides any font-lock background coloring.

Low coloring uses the same background color for all submode regions. This color is specified with the face mmm-default-submode-face (see Faces (The Emacs Manual)) which can be customized, either through the Emacs ``customize'' interface or using direct Lisp commands such as set-face-background.  Of course, other aspects of the face can also be set, such as the foreground color, bold, underline, etc.  These are more likely to conflict with font-lock, however, so only a background color is recommended.

High coloring uses multiple background colors, depending on the function of the submode region.  The recognized functions and their meanings are as follows:

init
     Code that is executed at the beginning of (something), as initialization of some sort.

cleanup
     Code that is executed at the end of (something), as some sort of clean up facility.

declaration
     Code that provides declarations of some sort, perhaps global or local arguments, variables, or methods.

comment
     Text that is not executed as code, but instead serves to document the code around it.  Submode regions of this function often use a mode such as Text Mode rather than a programming language mode.

output
     An expression that is evaluated and its value interpolated into the output produced.

code
     Executed code not falling under any other category.

special
     Submode regions not falling under any other category, such as component calls.

The different background colors are provided by the faces mmm-FUNCTION-submode-face, which can be customized in the same way as mmm-default-submode-face.

Preferred Major Modes
=====================

Certain of the supplied submode classes know only the language that certain sections are written in, but not what major mode you prefer to use to edit such code.  For example, many people prefer CPerl mode over Perl mode; you may have a special mode for Javascript or just use C++ mode.  This variable allows you to tell submodes such as Mason (see Mason) and Embedded Javascript (see Javascript) what major mode to use for the submodes:

 -- User Option: mmm-major-mode-preferences
     The elements of this list are cons cells of the form (LANGUAGE . MODE).  LANGUAGE should be a symbol such as perl, html-js, or java, while MODE should be the name of a major mode such as perl-mode, cperl-mode, javascript-mode, or c++-mode.

     You probably won't have to set this variable at all; MMM tries to make intelligent guesses about what modes you prefer.  For example, if a function called javascript-mode exists, it is chosen, otherwise c++-mode is used.  Similarly for jde-mode and java-mode.

If you do need to change the defaults, you may find the following function convenient.

 -- Function: mmm-set-major-mode-preferences LANGUAGE MODE &optional DEFAULT
     Set the preferred major mode for LANGUAGE to MODE.  If there is already a mode specified for LANGUAGE, and DEFAULT is nil or unsupplied, then it is changed.  If DEFAULT is non-nil, then any existing mode is unchanged. This is used by packages to ensure that some mode is present, but not override any user-specified mode.  If you are not writing a submode class, you should ignore the third argument.

Thus, for example, to use my-java-mode for Java code, you would use the following line:

     (mmm-set-major-mode-preferences 'java 'my-java-mode)

Customizing the Mode Line Display
=================================

By default, when in a submode region, MMM Mode changes the section of the mode line (see Mode Line (The Emacs Manual)) that normally displays the major mode name---for example, HTML---to instead show both the dominant major mode and the currently active submode---for example, HTML[CPerl].  You can change this format, however.

 -- User Option: mmm-submode-mode-line-format
     The value of this variable should be a string containing one or both of the escape sequences ~M and ~m.  The string displayed in the major mode section of the mode line when in a submode is obtained by replacing all occurrences of ~M with the dominant major mode name and ~m with the currently active submode name.  For example, to display only the currently active submode, set this variable to ~m.  The default value is ~M[~m].

The MMM minor mode also normally displays the string MMM in the minor mode section of the mode line to indicate when it is active.  You can customize or disable this as well.

 -- User Option: mmm-mode-string
     This string is displayed in the minor mode section of the mode line when the MMM minor mode is active.  If nonempty, it should begin with a space to separate the MMM indicator from that of other minor modes.  To eliminate the indicator entirely, set this variable to the empty string.

Customizing the MMM Mode Key Bindings
=====================================

The default MMM Mode key bindings are explained in MMM Mode Keys, and in Insertion.  There are a couple of ways to customize these bindings.

 -- User Option: mmm-mode-prefix-key
     The value of this variable (default is C-c %) should be a key sequence to use as the prefix for the MMM Mode keymap.  Minor modes typically use C-c followed by a punctuation character, but you can change it to any user-available key sequence.  To have an effect, this variable should be set before MMM Mode is loaded.

 -- User Option: mmm-use-old-command-keys
     When this variable is nil, MMM Mode commands use the control modifier and insertion keys no modifier.  Any other value switches the two, so that mmm-parse-buffer, for example, is bound to C-c % b, while perl-section insertion in the Mason class is bound to C-c % C-p.  This variable should be set before MMM Mode is loaded to have an effect.

When MMM is loaded, it uses the value of mmm-use-old-command-keys to set the values of the variables mmm-command-modifiers and mmm-insert-modifiers, so if you prefer you can set these variables instead.  They should each be a list of key modifiers, such as (control) or ().  The Meta modifier is used in some of the command and insertion keys, so it should not be used, and the Shift modifier is not particularly portable between Emacsen---if it works for you, feel free to use it.  Other modifiers, such as Hyper and Super, are not universally available, but are valid when present.

Changing Saved Local Variables
==============================

A lot of the functionality of MMM Mode---that which makes the major mode appear to change---is implemented by saving and restoring the values of local variables, or pseudo-variables.  You can customize what variables are saved, and how, with the following variable.

 -- Variable: mmm-save-local-variables
     At its simplest, this is a list each of whose elements is a buffer-local variable whose value is saved and restored for each major mode.  Each elements can also, however, be a list whose first element is the variable symbol and whose subsequent elements specify how and where the variable is to be saved.  The second element of the list, if present, should be one of the symbols global, buffer, or region.  If not present, the default value is global.  The third element, if present, should be a list of major mode symbols in which to save the variable.  In the list form, the variable symbol itself can be replaced with a cons cell of two functions, one to get the value and one to set the value.  This is called a ``pseudo-variable''.

Globally saved variables are the same in all (MMM-controlled) buffers and submode regions of each major mode listed in the third argument, or all major modes if it is t or not present.  Buffer-saved variables are the same in all submode regions of a given major mode in each buffer, and region-saved variables can be different for each submode region.

Pseudo-variables are used, for example, to save and restore the syntax table (see Syntax (The Emacs Manual)) and mode keymaps (see Keymaps (The Emacs Manual)).

Changing the Supplied Submode Classes
=====================================

If you need to use MMM with a syntax for which a submode class is not supplied, and you have some facility with Emacs Lisp, you can write your own; see Writing Classes.  However, sometimes you will only want to make a slight change to one of the supplied submode classes.  You can do this, after that class is loaded, with the following functions.

 -- Function: mmm-set-class-parameter CLASS PARAM VALUE
     Set the value of the keyword parameter PARAM of the submode class CLASS to VALUE.  See Writing Classes, for an explanation of the meaning of each keyword parameter.  This creates a new parameter if one is not already present in the class.

 -- Function: mmm-get-class-parameter CLASS PARAM
     Get the value of the keyword parameter PARAM for the submode class CLASS.  Returns nil if there is no such parameter.

Hooks Provided by MMM Mode
==========================

MMM Mode defines several hook variables (see Hooks (The Emacs Manual)) which are run at different times.  The most often used is mmm-major-mode-hook which is described in Major Mode Hook, but there are a couple others.

 -- Variable: mmm-mode-hook
     This normal hook is run whenever MMM Mode is enabled in a buffer.

 -- Variable: mmm-MAJOR-MODE-hook
     This is actually a whole set of hook variables, a different one for every major mode.  Whenever MMM Mode is enabled in a buffer, the corresponding hook variable for the dominant major mode is run.

 -- Variable: mmm-SUBMODE-submode-hook
     Again, this is a set of one hook variable per major mode.  These hooks are run whenever a submode region of the corresponding major mode is created in any buffer, with point at the start of the new submode region.

 -- Variable: mmm-CLASS-class-hook
     This is a set of one hook variable per submode class.  These hooks are run when a submode class is first applied to a given buffer.

Submode classes also have a :creation-hook parameter which should be a function to run whenever a submode region is created with that class, with point at the beginning of the submode region.  This can be set for supplied submode classes with mmm-set-class-parameter; Changing Classes.

Supplied Submode Classes
************************

This chapter describes the submode classes that are supplied with MMM Mode.

Mason: Perl in HTML
===================

Mason is a syntax to embed Perl code in HTML and other documents.  See http://www.masonhq.com for more information.  The submode class for Mason components is called `mason' and is loaded on demand from `mmm-mason.el'.  The current Mason class is intended to correctly recognize all syntax valid in Mason 0.896.  There are insertion keys for most of the available syntax; use mmm-insertion-help (C-c % h by default) with Mason on to get a list.

If you want to have mason submodes automatically in all Mason files, you can use automatic mode and filename associations; the details depend on what you call your Mason components and what major mode you use. See Mode-Ext Classes.  If you use an extension for your Mason files that emacs does not automatically place in your preferred HTML Mode, you will probably want to associate that extension with your HTML Mode as well; Choosing Modes (The Emacs Manual).  This also goes for ``special'' Mason files such as autohandlers and dhandlers.

The Perl mode used is controlled by the user: see Preferred Modes. The default is to use CPerl mode, if present.  Unfortunately, there are also certain problems with CPerl mode in submode regions.  (Not to say that the original perl-mode would do any better---it hasn't been much tried.)  First of all, the first line of a Perl section is usually indented as if it were a continuation line.  A fix for this is to start with a semicolon on the first line.  The insertion key commands do this whenever the Mason syntax allows it.

     <%perl>;
     print $var;
     </%perl>

In addition, some users have reported that the CPerl indentation sometimes does not work. This problem has not yet been tracked down, however, and more data about when it happens would be helpful.

Some people have reported problems using PSGML with Mason.  Adding the following line to a .emacs file should suffice to turn PSGML off and cause emacs to use a simpler HTML mode:

     (autoload 'html-mode "sgml-mode" "HTML Mode" t)

Earlier versions of PSGML may require instead the following fix:

     (delete '("\\.html$" . sgml-html-mode) auto-mode-alist)
     (delete '("\\.shtml$" . sgml-html-mode) auto-mode-alist)

Other users report using PSGML with Mason and MMM Mode without difficulty.  If you don't have problems and want to use PSGML, you may need to replace html-mode in the suggested code with sgml-html-mode.  (Depending on your version of PSGML, this may not be necessary.)  Similarly, if you are using XEmacs and want to use the alternate HTML mode hm--html-mode, replace html-mode with that symbol.

One problem that crops up when using PSGML with Mason is that even ignoring the special tags and Perl code (which, as I've said, haven't caused me any problems), Mason components often are not a complete SGML document.  For instance, my autohandlers often say

     <body>
       <% $m->call_next %>
     </body>

in which case the actual components contain no doctype declaration, <html>, <head>, or <body>, confusing PSGML.  One solution I've found is to use the variable sgml-parent-document in such incomplete components; try, for example, these lines at the end of a component.

     %# Local Variables:
     %# sgml-parent-document: ("autohandler" "body" nil ("body"))
     %# sgml-doctype: "/top/level/autohandler"
     %# End:

This tells PSGML that the current file is a sub-document of the file autohandler and is included inside a <body> tag, thus alleviating its confusion.

Elisp in a Local Variables List
===============================

Emacs allows the author of a file to specify major and minor modes to be used while editing that file, as well as specifying values for other local Elisp variables, with a File Variables list.  See File Variables (The Emacs Manual).  Since file variables values are Elisp objects (and with the eval special ``variable'', they are forms to be evaluated), one might want to edit them in emacs-lisp-mode.  The submode class file-variables allows this, and is suitable for turning on in a given file with mmm-classes, or in all files with mmm-global-classes.

Here-documents
==============

One of the long-time standard syntaxes for outputting large amounts of code (or text, or HTML, or whatever) from a script (notably shell scripts and Perl scripts) is the here-document syntax:

     print <<END_HTML;
     <html>
       <head>
         <title>Test Page</title>
       </head>
       <body>
     END_HTML

The here-doc submode class recognizes this syntax, and can even guess the correct submode to use in many cases.  For instance, it would put the above example in html-mode, noticing the string HTML in the name of the here-document.  If you use less than evocative here-document names, or if the submode is recognized incorrectly for any other reason, you can tell it explicitly what submode to use.

 -- User Option: mmm-here-doc-mode-alist
     The value of this variable should be an alist, each element a cons pair associating a regular expression to a submode symbol.  Whenever a here-document name matches one of these regexps, the corresponding submode is applied.  For example, if this variable contains the element ("CODE" . cc-mode), then any here-document whose name contains the string CODE will be put in cc-mode.  The value of this variable overrides any guessing that the here-doc submode class would do otherwise.

Javascript in HTML
==================

The submode class html-js allows for embedding Javascript code in HTML documents.  It recognizes both this syntax:

     <script language="Javascript">
     function foo(...) {
        ...
     }
     </script>

and this syntax:

     <input type="button" onClick="validate();">

The mode used for Javascript regions is controlled by the user; see Preferred Modes.

CSS embedded in HTML
====================

CSS (Cascading Style Sheets) can also be embedded in HTML.  The embedded-css submode class recognizes this syntax:

     <style>
     h1 {
        ...
     }
     </style>

It uses css-mode if present, c++-mode otherwise.  This can be customized: see Preferred Modes.

Embperl: More Perl in HTML
==========================

Embperl is another syntax for embedding Perl in HTML.  See http://perl.apache.org/embperl for more information.  The embperl submode class recognizes most if not all of the Embperl embedding syntax.  Its Perl mode is also controllable by the user; see Preferred Modes.

ePerl: General Perl Embedding
=============================

Yet another syntax for embedding Perl is called ePerl.  See http://www.engelschall.com/sw/eperl/ for more information.  The eperl submode class handles this syntax, using the Perl mode specified by the user; see Preferred Modes.

JSP: Java Embedded in HTML
==========================

JSP (Java Server Pages) is a syntax for embedding Java code in HTML. The submode class jsp handles this syntax, using a Java mode specified by the user; see Preferred Modes.  The default is jde-mode if present, otherwise java-mode.

RPM Spec Files
==============

mmm-rpm.el contains the definition of an MMM Mode submode class for editing shell script sections within RPM (Redhat Package Manager) spec files.  It is recommended for use in combination with rpm-spec-mode.el by Stig Bjørlykke <stigb@tihlde.hist.no> and Steve Sanbeg <sanbeg@dset.com> (http://www.xemacs.org/~stigb/rpm-spec-mode.el).

Suggested setup code:

     (add-to-list 'mmm-mode-ext-classes-alist
                  '(rpm-spec-mode "\\.spec\\'" rpm-sh))

Thanks to Marcus Harnisch <Marcus.Harnisch@gmx.net> for contributing this submode class.

Noweb literate programming
==========================

mmm-noweb.el contains the definition of an MMM Mode submode class for editing Noweb documents.  Most Noweb documents use \LaTeX for the documentation chunks.  Code chunks in Noweb are document-specific, and the mode may be set with a local variable setting in the document.  The variable MMM-NOWEB-CODE-MODE controls the global code chunk mode. Since Noweb files may have many languages in their code chunks, this mode also allows setting the mode by specifying a mode in the first line or two of a code chunk, using the normal Emacs first-line mode setting syntax.  Note that this first-line mode setting only matches a single word for the mode name, and does not support the variable name setting of the generalized first file line syntax.

% -*- mode: latex; mmm-noweb-code-mode: c++; -*-
% First chunk delimiter!
@
\noweboptions{smallcode}

\title{Sample Noweb File}
\author{Joe Kelsey\\
\nwanchorto{mailto:bozo@bozo.bozo}{\tt bozo@bozo.bozo}}
\maketitle

@
\section{Introduction}
Normal noweb documentation for the required [[*]] chunk.
<<*>>=
// C++ mode here!
// We might list the program here, or simply included chunks.
<<myfile.cc>>
@ %def myfile.cc

@
\section{[[myfile.cc]]}
This is [[myfile.cc]].  MMM noweb-mode understands code quotes in
documentation.
<<myfile.cc>>=
// This section is indented separately from previous.
@

@
\section{A Perl Chunk}
We need a Perl chunk.
<<myfile.pl>>=
#!/usr/bin/perl
# -*- perl -*-
# Each differently named chunk is flowed separately.
@

\section{Finish [[myfile.cc]]}
When we resume a previously defined chunk, they are indented together.
<<myfile.cc>>=
// Pick up where we left off...
@

The quoted code chunks inside documentation chunks are given the mode found in the variable MMM-NOWEB-QUOTE-MODE, if set, or the value in MMM-NOWEB-CODE-MODE otherwise.  Also, each quoted chunk is set to have a unique name to prevent them from being indented as a unit.

Suggested setup code:

     (mmm-add-mode-ext-class 'latex-mode "\\.nw\\'" 'noweb)
     (add-to-list 'auto-mode-alist '("\\.nw\\'" . latex-mode))

In mmm-noweb buffers, each differently-named code chunk has a different :name, allowing all chunks with the same name to get indented together.

This mode also supplies special paragraph filling operations for use in documentation areas of the buffer.  From a primary-mode (latex-mode, , emacs) region, pressing C-c % C-q will mark all submode regions with word syntax (mmm-word-other-regions), fill the current paragraph ((fill-paragraph justify)), and remove the syntax markings (mmm-undo-syntax-other-regions).

Thanks to Joe Kelsey <joe@zircon.seattle.wa.us> for contributing this class.

Writing Submode Classes
***********************

Sometimes (perhaps often) you may want to use MMM with a syntax for which it is suited, but for which no submode is supplied.  In such cases you may have to write your own submode class.  This chapter briefly describes how to write a submode class, from the basic to the advanced, with examples.

Writing Basic Submode Classes
=============================

Writing a submode class can become rather complex, if the syntax to match is complicated and you want to take advantage of some of MMM Mode's extra features.  But a simple submode class is not particularly difficult to write.  This section describes the basics of writing submode classes.

Submode classes are stored in the variable mmm-classes-alist. Each element of this list represents a single submode class.  For convenience, the function mmm-add-classes takes a list of submode classes and adds them all to this alist.  Each class is represented by a list containing the class name---a symbol such as mason or html-js---followed by pairs of keywords and arguments called a class specifier.  For example, consider the specifier for the submode class embedded-css:

     (mmm-add-classes
      '((embedded-css
         :submode css
         :face mmm-declaration-submode-face
         :front "<style[^>]*>"
         :back "</style>")))

The name of the submode is embedded-css, the first element of the list.  The rest of the list consists of pairs of keywords (symbols beginning with a colon) such as :submode and :front, and arguments, such as css and "<style[^>]*>".  It is the keywords and arguments that specify how the submode works.  The order of keywords is not important; all that matters is the arguments that follow them.

The three most important keywords are :submode, :front, and :back.  The argument following :submode names the major mode to use in submode regions.  It can be either a symbol naming a major mode, such as text-mode or c++-mode, or a symbol to look up in mmm-major-mode-preferences (see Preferred Modes) such as css, as in this case.

The arguments following :front and :back are regular expressions (see Regexps (The Emacs Manual)) that should match the delimiter strings which begin and end the submode regions.  In our example, CSS regions begin with a <style> tag, possibly with parameters, and end with a </style> tag.

The argument following :face specifies the face (background color) to use when mmm-submode-decoration-level is 2 (high coloring).  See Region Coloring, for a list of canonical available faces.

There are many more possible keywords arguments.  In the following sections, we will examine each of them and their uses in writing submode classes.

Matching Paired Delimiters
==========================

A simple pair of regular expressions does not always suffice to exactly specify the beginning and end of submode regions correctly.  For this reason, there are several other possible keyword/argument pairs which influence the matching process.

Many submode regions are marked by paired delimiters.  For example, the tags used by Mason (see Mason) include <%init>...</%init> and <%args>...</%args>.  It would be possible to write a separate submode class for each type of region, but there is an easier way: the keyword argument :save-matches.  If supplied and non-nil, it causes the regular expression :back, before being searched for, to be formatted by replacing all strings of the form ~N (where N is an integer) with the corresponding numbered subexpression of the match for :front.  As an example, here is an excerpt from the here-doc submode class.  See Here-documents, for more information about this submode.

     :front "<<\\([a-zA-Z0-9_-]+\\)"
     :back "^~1$"
     :save-matches 1

The regular expression for :front matches << followed by a string of one or more alphanumeric characters, underscores, and dashes. The latter string, which happens to be the name of the here-document, is saved as the first subexpression, since it is surrounded by \(...\).  Then, because the value of :save-matches is present and non-nil, the string ~1 is replaced in the value of :back by the name of the here-document, thus creating a regular expression to match the correct ending delimiter.

Placing Submode Regions Precisely
=================================

Normally, a submode region begins immediately after the end of the string matching the :front regular expression and ends immediately before the beginning of the string matching the :back regular expression.  This can be changed with the keywords :include-front and :include-back.  If their arguments are nil, or they do not appear, the default behavior is unchanged. But if the argument of :include-front (respectively, :include-back) is non-nil, the submode region will begin (respectively, end) immediately before (respectively, after) the string matching the :front (respectively, :back) regular expression.  In other words, these keywords specify whether or not the delimiter strings are included in the submode region.

When :front and :back are regexps, the delimiter is normally considered to be the entire matched region.  This can be changed using the :front-match and :back-match keywords.  The values of the keywords is a number specifying the submatch.  This defaults to zero (specifying the whole regexp).

Two more keywords which affect the placement of the region :front-offset and :back-offset, which both take integers as arguments.  The argument of :front-offset (respectively, :back-offset) gives the distance in characters from the beginning (respectively, ending) location specified so far, to the actual point where the submode region begins (respectively, ends).  For example, if :include-front is nil or unsupplied and :front-offset is 2, the submode region will begin two characters after the end of the match for :front, and if :include-back is non-nil and :back-offset is -1, the region will end one character before the end of the match for :back.

In addition to integers, the arguments of :front-offset and :back-offset can be functions which are invoked to move the point from the position specified by the matches and inclusions to the correct beginning or end of the submode region, or lists whose elements are either functions or numbers and whose effects are applied in sequence. To help disentangle these options, here is another excerpt from the here-doc submode class:

     :front "<<\\([a-zA-Z0-9_-]+\\)"
     :front-offset (end-of-line 1)
     :back "^~1$"
     :save-matches 1

Here the value of :front-offset is the list (end-of-line 1), meaning that from the end of the match for :front, go to the end of the line, and then one more character forward (thus to the beginning of the next line), and begin the submode region there.  This coincides with the normal behavior of here-documents: they begin on the following line and go until the ending flag.

If the :back should not be able to start a new submode region, set the :end-not-begin keyword to non-nil.

Defining Groups of Submodes
===========================

Sometimes more than one submode class is required to accurately reflect the behavior of a single type of syntax.  For example, Mason has three very different types of Perl regions: blocks bounded by matched tags such as <%perl>...</%perl>, inline output expressions bounded by <%...%>, and single lines of code which simply begin with a % character.  In cases like these, it is possible to specify an ``umbrella'' class, to turn all these classes on or off together.

 -- Function: mmm-add-group GROUP CLASSES
     The submode classes CLASSES, which should be a list of lists, similar to what might be passed to mmm-add-classes, are added just as by that function.  Furthermore, another class named GROUP is added, which encompasses all the classes in CLASSES.

Technically, an group class is specified with a :classes keyword argument, and the subsidiary classes are given a non-nil :private keyword argument to make them invisible.  But in general, all you should ever need to know is how to invoke the function above.

 -- Function: mmm-add-to-group GROUP CLASSES
     Adds a list of classes to an already existing group.  This can be used, for instance, to add a new quoting definition to HTML-JS using this example to add the quote characters ``%=%'':

          (mmm-add-to-group 'html-js '((js-html
          			     :submode javascript
          			     :face mmm-code-submode-face
          			     :front "%=%"
          			     :back "%=%"
          			     :end-not-begin t)))

Calculating the Correct Submode
===============================

In most cases, the author of a submode class will know in advance what major mode to use, such as text-mode or c++-mode.  If there are multiple possible modes that the user might desire, then mmm-major-mode-preferences should be used (see Preferred Modes).  The function mmm-set-major-mode-preferences can be used, with a third argument, to ensure than the mode is present.

In some cases, however, the author has no way of knowing in advance even what language the submode region will be in.  The here-doc class is one of these.  In such cases, instead of the :submode keyword, the :match-submode keyword must be used.  Its argument should be a function, probably written by the author of the submode class, which calculates what major mode each region should use.

It is invoked immediately after a match is found for :front, and is passed one argument: a string representing the front delimiter. Normally this string is simply whatever was matched by :front, but this can be changed with the keyword :front-form (see Delimiters).  The function should then return a symbol that would be a valid argument to :submode: either the name of a mode, or that of a language to look up a preferred mode.  If it detects an invalid match---for example, the user has specified a mode which is not available---it should (signal 'mmm-no-matching-submode nil).

Since here-documents can contain code in any language, the here-doc submode class uses :match-submode rather than :submode.  The function it uses is mmm-here-doc-get-mode, defined in mmm-sample.el, which inspects the name of the here-document for flags indicating the proper mode.  For example, this code should probably be in perl-mode (or cperl-mode):

     print <<PERL;
     s/foo/bar/g;
     PERL

This function is also a good example of proper elisp hygiene: when writing accessory functions for a submode class, they should usually be prefixed with mmm- followed by the name of the submode class, to avoid namespace conflicts.

Calculating the Correct Highlight Face
======================================

As explained in Basic Classes, the keyword :face should be used to specify which of the standard submode faces (see Region Coloring) a submode region should be highlighted with under high decoration.  However, sometimes the function of a region can depend on the form of the delimiters as well.  In this case, a more flexible alternative to :face is :match-face.  Its value can be a function, which is called with one argument---the form of the front delimiter, as with :match-submode---and should return the face to use.  A more common value for :match-face is an association list, a list of pairs (DELIM . FACE), each specifying that if the delimiter is DELIM, the corresponding region should be highlighted with FACE.  For example, here is an excerpt from the embperl submode class:

     :submode perl
     :front "\\[\\([-\\+!\\*\\$]\\)"
     :back "~1\\]"
     :save-matches 1
     :match-face (("[+" . mmm-output-submode-face)
                  ("[-" . mmm-code-submode-face)
                  ("[!" . mmm-init-submode-face)
                  ("[*" . mmm-code-submode-face)
                  ("[$" . mmm-special-submode-face))

Thus, regions beginning with [+ are highlighted as output expressions, which they are, while [- and [* regions are highlighted as simple executed code, and so on.  Note that MMM-SUBMODE-DECORATION-LEVEL must be set to 2 (high decoration) for different faces to be displayed.

Specifying Insertion Commands
=============================

As described in Insertion, submode classes can specify key sequences which automatically insert submode regions, with delimiters already in place.  This is done by the keyword argument :insert. Its value should be a list, each element of which specifies a single insertion key sequence.  As an example, consider the following insertion key sequence specifier, from the embperl submode class:

     (?p embperl "Region Type (Character): "
         @ "[" str @ " " _ " " @ str "]" @)

As you can see, the specifier is a list.  The first element of the list is the character p.  (The question mark tells Emacs that this is a character object, not a one-character symbol.)  In general, the first element can be any key, including both characters such as ?p and function keys such as return.  It can also be a dotted pair in which the first element is a modifier symbol such as meta, and the second is a character or function key.  The use of any other modifier than meta is discouraged, as `mmm-insert-modifiers' is sometimes set to \(control), and other modifiers are not very portable. The second element is a symbol identifying this key sequence.  The third element is a prompt string which is used to ask the user for input when this key sequence is invoked.  If it is nil, the user is not prompted.

The rest of the list specifies the actual text to be inserted, where the submode region and delimiters should be, and where the point should end up.  (Actually, this string is simply passed to skeleton-insert; see the documentation string of that function for more details on the permissible elements of such a skeleton.)  Strings and variable names are inserted and interpolated.  The value entered by the user when prompted, if any, is available in the variable str.  The final location of the point (or the text around which the region is to be wrapped) is marked with a single underscore _.  Finally, the @-signs mark the delimiters and submode regions.  There should be four @-signs: one at the beginning of the front delimiter, one at the beginning of the submode region, one at the end of the submode region, and one at the end of the back delimiter.

The above key sequence, bound by default to C-c % p, always prompts the user for the type of region to insert.  It can also be convenient to have separate key sequences for each type of region to be inserted, such as C-c % + for [+...+] regions, C-c % - for [-...-] regions, and so on.  So that the whole skeleton doesn't have to be written out half a dozen times, there is a shortcut syntax, as follows:

     (?+ embperl+ ?p . "+")

If the key sequence specification is a dotted list with four elements, as this example is, it means to use the skeleton defined for the key sequence given as the third element (?p), but to pass it the fourth (dotted) element ("+") as the `str' variable; the user is not prompted.

Giving Names to Submode Regions for Grouping
============================================

Submode regions can be given ``names'' which are used for grouping. Names are always strings and are compared as strings.  Regions with the same name are considered part of the same chunk of code.  This is used by the syntax and fontification functions.  Unnamed regions are not grouped with any others.

By default, regions are nameless, but with the :match-name keyword argument a name can be supplied.  This argument must be a string or a function.  If it is a function, it is passed a string representing the front delimiter found, and must return the name to use.  If it is a string, it is used as-is for the name, unless :save-name has a non-nil value, in which case expressions such as ~1 are substituted with the corresponding matched subexpression from :front.  This is the same as how :back is interpreted when :save-matches is non-nil.

As a special optimization for region insertion (see Insertion Commands), the argument :skel-name can be set to a non-nil value, in which case the insertion code will use the user-prompted string value as the region name, instead of going through the normal matching procedure.

Other Hooks into the Scanning Process
=====================================

Sometimes, even the flexibility allowed by all the keyword arguments discussed so far is insufficient to correctly match submode regions. There are several other keyword arguments which accept custom functions to be invoked at various points in the MMM-ification process.

First of all, the arguments of :front and :back, in addition to regular expressions, can be themselves functions.  Such functions should ``act like'' a regular expression search: they should start searching at point, take one argument as a limit for the search, and return its result by setting the match data (presumably by calling some regexp matching function).

This is rarely necessary, however, because often all that is needed is a simple regexp search, followed by some sort of verification.  The keyword arguments :front-verify and :back-verify, if supplied, may be functions which are invoked after a match is found for :front or :back, respectively, and should inspect the match data (such as with match-string) and return non-nil if a submode region should be begun at this match, nil if this match should be ignored and the search continue after it.

The keyword argument :creation-hook, if supplied, should be a function that is invoked whenever a submode region of this class is created, with point at the beginning of the new region.  This can be used, for example, to set local variables appropriately.

Finally, the entire MMM-ification process has a ``back door'' which allows class authors to take control of the entire thing.  If the keyword argument :handler is supplied, it overrides any other processing and is called, and passed all other class keyword arguments, instead of mmm-ify to create submode regions.  If you need to write a handler function, I suggest looking at the source for mmm-ify to get an idea of what must be done.

Controlling the Delimiter Regions and Forms
===========================================

MMM also makes overlays for the delimiter regions, to keep track of their position and form.  Normally, the front delimiter overlay starts at the beginning of the match for :front and ends at the beginning of the submode region overlay, while the back delimiter overlay starts at the end of the submode region overlay and ends at the end of the match for :back.  You can supply offsets from these positions using the keyword arguments :front-delim and :back-delim, which take values of the same sort as :front-offset and :back-offset.

In addition, the delimiter regions can be in a major mode of their own.  There are usually only two meaningful modes to use: the primary mode or a non-mode like fundamental-mode.  These correspond to the following two situations:

  * If the delimiter syntax which specifies the submode regions is something added to the syntax of the primary mode by a pre-interpreter, then the delimiter regions should be in a non-mode. This is the case, for example, with all server-side HTML script extensions, such as see Mason, see Embperl, and see ePerl. It is also the case for literate programming such as see Noweb. This is the default behavior.  The non-mode used is controlled by the variable mmm-delimiter-mode, which defaults to fundamental-mode.

  * If, on the other hand, the delimiter syntax and inclusion of different modes is an intrinsic part of the primary mode, then the delimiter regions should remain in the primary mode.  This is the case, for example, with see Embedded CSS, and see Javascript, since the <style> and <script> tags are perfectly valid HTML.  In this case, you should give the keyword parameter :delimiter-mode with a value of nil, meaning to use the primary mode.

The keyword parameter :delimiter-mode can be given any major mode as an argument, but the above two situations should cover the vast majority of cases.

The delimiter regions can also be highlighted, if you wish.  The keyword parameters :front-face and :back-face may be faces specifying how to highlight these regions under high decoration.  Under low decoration, the value of the variable mmm-delimiter-face is used (by default, nothing), and of course under no decoration there is no coloring.

Finally, for each submode region overlay, MMM Mode stores the ``form'' of the front and back delimiters, which are regular expressions that match the delimiters.  At present these are not used for much, but in the future they may be used to help with automatic updating of regions as you type.  Normally, the form stored is the result of evaluating the expression (regexp-quote (match-string 0)) after each match is found.

You can customize this with the keyword argument :front-form (respectively, :back-form).  If it is a string, it is used verbatim for the front (respectively, back) form.  If it is a function, that function is called and should inspect the match data and return the regular expression to use as the form.

In addition, the form itself can be set to a function, by giving a one-element list containing only that function as the argument to :front-form or :back-form.  Such a function should take 1-2 arguments.  The first argument is the overlay to match the delimiter for.  If the second is non-nil, it means to insert the delimiter and adjust the overlay; if nil it means to match the delimiter and return the result in the match data.

Miscellaneous Other Keyword Arguments
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You can specify whether delimiter searches should be case-sensitive with the keyword argument :case-fold-search.  It defaults to t, meaning that case should be ignored.  See the documentation for the variable case-fold-search.

Indices
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