+File: lispref.info, Node: Gutter Intro, Next: Creating Gutter, Prev: Gutter, Up: Gutter
+
+Gutter Intro
+============
+
+ A "gutter" is a rectangle displayed along one edge of a frame. It
+can contain arbitrary text or graphics. It could be considered a
+generalization of a toolbar, although toolbars are not currently
+implemented using gutters.
+
+ In XEmacs, a gutter can be displayed along any of the four edges of
+the frame, and two or more different edges can be displaying gutters
+simultaneously. The contents, thickness, and visibility of the gutters
+can be controlled separately, and the values can be per-buffer,
+per-frame, etc., using specifiers (*note Specifiers::).
+
+ Normally, there is one gutter displayed in a frame. Usually, this is
+the default gutter, containing buffer tabs, but modes cab override this
+and substitute their own gutter. This default gutter is usually
+positioned along the top of the frame, but this can be changed using
+`set-default-gutter-position'.
+
+ Note that, for each of the gutter properties (contents, thickness,
+and visibility), there is a separate specifier for each of the four
+gutter positions (top, bottom, left, and right), and an additional
+specifier for the "default" gutter, i.e. the gutter whose position is
+controlled by `set-default-gutter-position'. The way this works is
+that `set-default-gutter-position' arranges things so that the
+appropriate position-specific specifiers for the default position
+inherit from the corresponding default specifiers. That way, if the
+position-specific specifier does not give a value (which it usually
+doesn't), then the value from the default specifier applies. If you
+want to control the default gutter, you just change the default
+specifiers, and everything works. A package such as VM that wants to
+put its own gutter in a different location from the default just sets
+the position-specific specifiers, and if the user sets the default
+gutter to the same position, it will just not be visible.
+
+\1f
+File: lispref.info, Node: Creating Gutter, Next: Gutter Descriptor Format, Prev: Gutter Intro, Up: Gutter
+
+Creating Gutter
+===============
+
+ - Function: make-gutter-specifier spec-list
+ Return a new `gutter' specifier object with the given specification
+ list. SPEC-LIST can be a list of specifications (each of which is
+ a cons of a locale and a list of instantiators), a single
+ instantiator, or a list of instantiators. *Note Specifiers::, for
+ more information about specifiers.
+
+ Gutter specifiers are used to specify the format of a gutter. The
+ values of the variables `default-gutter', `top-gutter',
+ `left-gutter', `right-gutter', and `bottom-gutter' are always
+ gutter specifiers.
+
+ Valid gutter instantiators are called "gutter descriptors" and are
+ either strings or property-lists of strings. See `default-gutter'
+ for a description of the exact format.
+
+ - Function: make-gutter-size-specifier spec-list
+ Return a new `gutter-size' specifier object with the given spec
+ list. SPEC-LIST can be a list of specifications (each of which is
+ a cons of a locale and a list of instantiators), a single
+ instantiator, or a list of instantiators. *Note Specifiers::, for
+ more information about specifiers.
+
+ Gutter-size specifiers are used to specify the size of a gutter.
+ The values of the variables `default-gutter-size',
+ `top-gutter-size', `left-gutter-size', `right-gutter-size', and
+ `bottom-gutter-size' are always gutter-size specifiers.
+
+ Valid gutter-size instantiators are either integers or the special
+ symbol `autodetect'. If a gutter-size is set to `autodetect' them
+ the size of the gutter will be adjusted to just accommodate the
+ gutters contents. `autodetect' only works for top and bottom
+ gutters.
+
+ - Function: make-gutter-visible-specifier spec-list
+ Return a new `gutter-visible' specifier object with the given spec
+ list. SPEC-LIST can be a list of specifications (each of which is
+ a cons of a locale and a list of instantiators), a single
+ instantiator, or a list of instantiators. *Note Specifiers::, for
+ more information about specifiers.
+
+ Gutter-visible specifiers are used to specify the visibility of a
+ gutter. The values of the variables `default-gutter-visible-p',
+ `top-gutter-visible-p', `left-gutter-visible-p',
+ `right-gutter-visible-p', and `bottom-gutter-visible-p' are always
+ gutter-visible specifiers.
+
+ Valid gutter-visible instantiators are `t', `nil' or a list of
+ symbols. If a gutter-visible instantiator is set to a list of
+ symbols, and the corresponding gutter specification is a
+ property-list strings, then elements of the gutter specification
+ will only be visible if the corresponding symbol occurs in the
+ gutter-visible instantiator.
+
+\1f
+File: lispref.info, Node: Gutter Descriptor Format, Next: Specifying a Gutter, Prev: Creating Gutter, Up: Gutter
+
+Gutter Descriptor Format
+========================
+
+ The contents of a gutter are specified using a "gutter descriptor".
+The format of a gutter descriptor is a list of "gutter button
+descriptors". Each gutter button descriptor is a vector in one of the
+following formats:
+
+ * `[GLYPH-LIST FUNCTION ENABLED-P HELP]'
+
+ * `[:style 2D-OR-3D]'
+
+ * `[:style 2D-OR-3D :size WIDTH-OR-HEIGHT]'
+
+ * `[:size WIDTH-OR-HEIGHT :style 2D-OR-3D]'
+
+ Optionally, one of the gutter button descriptors may be `nil'
+instead of a vector; this signifies the division between the gutter
+buttons that are to be displayed flush-left, and the buttons to be
+displayed flush-right.
+
+ The first vector format above specifies a normal gutter button; the
+others specify blank areas in the gutter.
+
+ For the first vector format:
+
+ * GLYPH-LIST should be a list of one to six glyphs (as created by
+ `make-glyph') or a symbol whose value is such a list. The first
+ glyph, which must be provided, is the glyph used to display the
+ gutter button when it is in the "up" (not pressed) state. The
+ optional second glyph is for displaying the button when it is in
+ the "down" (pressed) state. The optional third glyph is for when
+ the button is disabled. The last three glyphs are for displaying
+ the button in the "up", "down", and "disabled" states,
+ respectively, but are used when the user has called for captioned
+ gutter buttons (using `gutter-buttons-captioned-p'). The function
+ `gutter-make-button-list' is useful in creating these glyph lists.
+
+ * Even if you do not provide separate down-state and disabled-state
+ glyphs, the user will still get visual feedback to indicate which
+ state the button is in. Buttons in the up-state are displayed
+ with a shadowed border that gives a raised appearance to the
+ button. Buttons in the down-state are displayed with shadows that
+ give a recessed appearance. Buttons in the disabled state are
+ displayed with no shadows, giving a 2-d effect.
+
+ * If some of the gutter glyphs are not provided, they inherit as
+ follows:
+
+ UP: up
+ DOWN: down -> up
+ DISABLED: disabled -> up
+ CAP-UP: cap-up -> up
+ CAP-DOWN: cap-down -> cap-up -> down -> up
+ CAP-DISABLED: cap-disabled -> cap-up -> disabled -> up
+
+ * The second element FUNCTION is a function to be called when the
+ gutter button is activated (i.e. when the mouse is released over
+ the gutter button, if the press occurred in the gutter). It can
+ be any form accepted by `call-interactively', since this is how it
+ is invoked.
+
+ * The third element ENABLED-P specifies whether the gutter button is
+ enabled (disabled buttons do nothing when they are activated, and
+ are displayed differently; see above). It should be either a
+ boolean or a form that evaluates to a boolean.
+
+ * The fourth element HELP, if non-`nil', should be a string. This
+ string is displayed in the echo area when the mouse passes over the
+ gutter button.
+
+ For the other vector formats (specifying blank areas of the gutter):
+
+ * 2D-OR-3D should be one of the symbols `2d' or `3d', indicating
+ whether the area is displayed with shadows (giving it a raised,
+ 3-d appearance) or without shadows (giving it a flat appearance).
+
+ * WIDTH-OR-HEIGHT specifies the length, in pixels, of the blank
+ area. If omitted, it defaults to a device-specific value (8
+ pixels for X devices).
+
+ - Function: gutter-make-button-list up &optional down disabled cap-up
+ cap-down cap-disabled
+ This function calls `make-glyph' on each arg and returns a list of
+ the results. This is useful for setting the first argument of a
+ gutter button descriptor (typically, the result of this function
+ is assigned to a symbol, which is specified as the first argument
+ of the gutter button descriptor).
+
+ - Function: check-gutter-button-syntax button &optional noerror
+ Verify the syntax of entry BUTTON in a gutter description list.
+ If you want to verify the syntax of a gutter description list as a
+ whole, use `check-valid-instantiator' with a specifier type of
+ `gutter'.
+
+\1f
+File: lispref.info, Node: Specifying a Gutter, Next: Other Gutter Variables, Prev: Gutter Descriptor Format, Up: Gutter
+
+Specifying a Gutter
+===================
+
+ In order to specify the contents of a gutter, set one of the
+specifier variables `default-gutter', `top-gutter', `bottom-gutter',
+`left-gutter', or `right-gutter'. These are specifiers, which means
+you set them with `set-specifier' and query them with `specifier-specs'
+or `specifier-instance'. You will get an error if you try to set them
+using `setq'. The valid instantiators for these specifiers are gutter
+descriptors, as described above. *Note Specifiers::, for more
+information.
+
+ Most of the time, you will set `default-gutter', which allows the
+user to choose where the gutter should go.
+
+ - Specifier: default-gutter
+ The position of this gutter is specified in the function
+ `default-gutter-position'. If the corresponding position-specific
+ gutter (e.g. `top-gutter' if `default-gutter-position' is `top')
+ does not specify a gutter in a particular domain, then the value
+ of `default-gutter' in that domain, of any, will be used instead.
+
+ Note that the gutter at any particular position will not be displayed
+unless its thickness (width or height, depending on orientation) is
+non-zero and its visibility status is true. The thickness is controlled
+by the specifiers `top-gutter-height', `bottom-gutter-height',
+`left-gutter-width', and `right-gutter-width', and the visibility
+status is controlled by the specifiers `top-gutter-visible-p',
+`bottom-gutter-visible-p', `left-gutter-visible-p', and
+`right-gutter-visible-p' (*note Other Gutter Variables::).
+
+ - Function: set-default-gutter-position position
+ This function sets the position that the `default-gutter' will be
+ displayed at. Valid positions are the symbols `top', `bottom',
+ `left' and `right'. What this actually does is set the fallback
+ specifier for the position-specific specifier corresponding to the
+ given position to `default-gutter', and set the fallbacks for the
+ other position-specific specifiers to `nil'. It also does the
+ same thing for the position-specific thickness and visibility
+ specifiers, which inherit from one of `default-gutter-height' or
+ `default-gutter-width', and from `default-gutter-visible-p',
+ respectively (*note Other Gutter Variables::).
+
+ - Function: default-gutter-position
+ This function returns the position that the `default-gutter' will
+ be displayed at.
+
+ You can also explicitly set a gutter at a particular position. When
+redisplay determines what to display at a particular position in a
+particular domain (i.e. window), it first consults the position-specific
+gutter. If that does not yield a gutter descriptor, the
+`default-gutter' is consulted if `default-gutter-position' indicates
+this position.
+
+ - Specifier: top-gutter
+ Specifier for the gutter at the top of the frame.
+
+ - Specifier: bottom-gutter
+ Specifier for the gutter at the bottom of the frame.
+
+ - Specifier: left-gutter
+ Specifier for the gutter at the left edge of the frame.
+
+ - Specifier: right-gutter
+ Specifier for the gutter at the right edge of the frame.
+
+ - Function: gutter-specifier-p object
+ This function returns non-`nil' if OBJECT is a gutter specifier.
+ Gutter specifiers are the actual objects contained in the gutter
+ variables described above, and their valid instantiators are
+ gutter descriptors (*note Gutter Descriptor Format::).
+
+\1f
+File: lispref.info, Node: Other Gutter Variables, Next: Common Gutter Widgets, Prev: Specifying a Gutter, Up: Gutter
+
+Other Gutter Variables
+======================
+
+ The variables to control the gutter thickness, visibility status, and
+captioned status are all specifiers. *Note Specifiers::.
+
+ - Specifier: default-gutter-height
+ This specifies the height of the default gutter, if it's oriented
+ horizontally. The position of the default gutter is specified by
+ the function `set-default-gutter-position'. If the corresponding
+ position-specific gutter thickness specifier (e.g.
+ `top-gutter-height' if `default-gutter-position' is `top') does
+ not specify a thickness in a particular domain (a window or a
+ frame), then the value of `default-gutter-height' or
+ `default-gutter-width' (depending on the gutter orientation) in
+ that domain, if any, will be used instead.
+
+ - Specifier: default-gutter-width
+ This specifies the width of the default gutter, if it's oriented
+ vertically. This behaves like `default-gutter-height'.
+
+ Note that `default-gutter-height' is only used when
+`default-gutter-position' is `top' or `bottom', and
+`default-gutter-width' is only used when `default-gutter-position' is
+`left' or `right'.
+
+ - Specifier: top-gutter-height
+ This specifies the height of the top gutter.
+
+ - Specifier: bottom-gutter-height
+ This specifies the height of the bottom gutter.
+
+ - Specifier: left-gutter-width
+ This specifies the width of the left gutter.
+
+ - Specifier: right-gutter-width
+ This specifies the width of the right gutter.
+
+ Note that all of the position-specific gutter thickness specifiers
+have a fallback value of zero when they do not correspond to the
+default gutter. Therefore, you will have to set a non-zero thickness
+value if you want a position-specific gutter to be displayed.
+
+ - Specifier: default-gutter-visible-p
+ This specifies whether the default gutter is visible. The
+ position of the default gutter is specified by the function
+ `set-default-gutter-position'. If the corresponding
+ position-specific gutter visibility specifier (e.g.
+ `top-gutter-visible-p' if `default-gutter-position' is `top') does
+ not specify a visible-p value in a particular domain (a window or
+ a frame), then the value of `default-gutter-visible-p' in that
+ domain, if any, will be used instead.
+
+ - Specifier: top-gutter-visible-p
+ This specifies whether the top gutter is visible.
+
+ - Specifier: bottom-gutter-visible-p
+ This specifies whether the bottom gutter is visible.
+
+ - Specifier: left-gutter-visible-p
+ This specifies whether the left gutter is visible.
+
+ - Specifier: right-gutter-visible-p
+ This specifies whether the right gutter is visible.
+
+ `default-gutter-visible-p' and all of the position-specific gutter
+visibility specifiers have a fallback value of true.
+
+ Internally, gutter thickness and visibility specifiers are
+instantiated in both window and frame domains, for different purposes.
+The value in the domain of a frame's selected window specifies the
+actual gutter thickness or visibility that you will see in that frame.
+The value in the domain of a frame itself specifies the gutter
+thickness or visibility that is used in frame geometry calculations.
+
+ Thus, for example, if you set the frame width to 80 characters and
+the left gutter width for that frame to 68 pixels, then the frame will
+be sized to fit 80 characters plus a 68-pixel left gutter. If you then
+set the left gutter width to 0 for a particular buffer (or if that
+buffer does not specify a left gutter or has a `nil' value specified for
+`left-gutter-visible-p'), you will find that, when that buffer is
+displayed in the selected window, the window will have a width of 86 or
+87 characters - the frame is sized for a 68-pixel left gutter but the
+selected window specifies that the left gutter is not visible, so it is
+expanded to take up the slack.
+
+ - Specifier: gutter-buttons-captioned-p
+ Whether gutter buttons are captioned. This affects which glyphs
+ from a gutter button descriptor are chosen. *Note Gutter
+ Descriptor Format::.
+
+ You can also reset the gutter to what it was when XEmacs started up.
+
+ - Constant: initial-gutter-spec
+ The gutter descriptor used to initialize `default-gutter' at
+ startup.
+
+\1f
+File: lispref.info, Node: Common Gutter Widgets, Prev: Other Gutter Variables, Up: Gutter
+
+Common Gutter Widgets
+=====================
+
+ A gutter can contain arbitrary text. So, for example, in an Info
+buffer you could put the title of the current node in the top gutter,
+and it would not scroll out of view in a long node. (This is an
+artificial example, since usually the node name is sufficiently
+descriptive, and Info puts that in the mode line.)
+
+ A more common use for the gutter is to hold some kind of active
+widget. The buffer-tab facility, available in all XEmacs frames,
+creates an array of file-folder-like tabs, which the user can click with
+the mouse to switch buffers. W3 uses a progress-bar widget in the
+bottom gutter to give a visual indication of the progress of
+time-consuming operations like downloading.
+
+* Menu:
+
+* Buffer Tabs:: Tabbed divider index metaphor for switching buffers.
+* Progress Bars:: Visual indication of operation progress.
+
+\1f
+File: lispref.info, Node: Buffer Tabs, Next: Progress Bars, Up: Common Gutter Widgets
+
+Buffer Tabs
+-----------
+
+ Not documented yet.
+
+\1f
+File: lispref.info, Node: Progress Bars, Prev: Buffer Tabs, Up: Common Gutter Widgets
+
+Progress Bars
+-------------
+
+ Not documented yet.
+
+\1f
+File: lispref.info, Node: Scrollbars, Next: Drag and Drop, Prev: Gutter, Up: Top
+
+Scrollbars
+**********
+
+ Not yet documented.
+
+\1f
+File: lispref.info, Node: Drag and Drop, Next: Modes, Prev: Scrollbars, Up: Top
+
+Drag and Drop
+*************
+
+ _WARNING_: the Drag'n'Drop API is still under development and the
+interface may change! The current implementation is considered
+experimental.
+
+ Drag'n'drop is a way to transfer information between multiple
+applications. To do this several GUIs define their own protocols.
+Examples are OffiX, CDE, Motif, KDE, MSWindows, GNOME, and many more.
+To catch all these protocols, XEmacs provides a generic API.
+
+ One prime idea behind the API is to use a data interface that is
+transparent for all systems. The author thinks that this is best
+archived by using URL and MIME data, cause any internet enabled system
+must support these for email already. XEmacs also already provides
+powerful interfaces to support these types of data (tm and w3).
+
+* Menu:
+
+* Supported Protocols:: Which low-level protocols are supported.
+* Drop Interface:: How XEmacs handles a drop from another application.
+* Drag Interface:: Calls to initiate a drag from XEmacs.
+
+\1f
+File: lispref.info, Node: Supported Protocols, Next: Drop Interface, Up: Drag and Drop
+
+Supported Protocols
+===================
+
+ The current release of XEmacs only support a small set of Drag'n'drop
+protocols. Some of these only support limited options available in the
+API.
+
+* Menu:
+
+* OffiX DND:: A generic X based protocol.
+* CDE dt:: Common Desktop Environment used on suns.
+* MSWindows OLE:: Mr. Gates way of live.
+* Loose ends:: The other protocols.
+
+\1f
+File: lispref.info, Node: OffiX DND, Next: CDE dt, Up: Supported Protocols
+
+OffiX DND
+---------
+
+ _WARNING_: If you compile in OffiX, you may not be able to use
+multiple X displays successfully. If the two servers are from
+different vendors, the results may be unpredictable.
+
+ The OffiX Drag'n'Drop protocol is part of a X API/Widget library
+created by Cesar Crusius. It is based on X-Atoms and ClientMessage
+events, and works with any X platform supporting them.
+
+ OffiX is supported if 'offix is member of the variable
+dragdrop-protocols, or the feature 'offix is defined.
+
+ Unfortunately it uses it's own data types. Examples are: File, Files,
+Exe, Link, URL, MIME. The API tries to choose the right type for the
+data that is dragged from XEmacs (well, not yet...).
+
+ XEmacs supports both MIME and URL drags and drops using this API. No
+application interaction is possible while dragging is in progress.
+
+ For information about the OffiX project have a look at
+http://leb.net/~offix/
+
+\1f
+File: lispref.info, Node: CDE dt, Next: MSWindows OLE, Prev: OffiX DND, Up: Supported Protocols
+
+CDE dt
+------
+
+ CDE stands for Common Desktop Environment. It is based on the Motif
+widget library. It's drag'n'drop protocol is also an abstraction of the
+Motif protocol (so it might be possible, that XEmacs will also support
+the Motif protocol soon).
+
+ CDE has three different types: file, buffer, and text. XEmacs only
+uses file and buffer drags. The API will disallow full URL drags, only
+file method URLs are passed through.
+
+ Buffer drags are always converted to plain text.
+
+\1f
+File: lispref.info, Node: MSWindows OLE, Next: Loose ends, Prev: CDE dt, Up: Supported Protocols
+
+MSWindows OLE
+-------------
+
+ Only allows file drags and drops.
+
+\1f
+File: lispref.info, Node: Loose ends, Prev: MSWindows OLE, Up: Supported Protocols
+
+Loose ends
+----------
+
+ The following protocols will be supported soon: Xdnd, Motif, Xde (if
+I get some specs), KDE OffiX (if KDE can find XEmacs windows).
+
+ In particular Xdnd will be one of the protocols that can benefit from
+the XEmacs API, cause it also uses MIME types to encode dragged data.
+
+\1f
+File: lispref.info, Node: Drop Interface, Next: Drag Interface, Prev: Supported Protocols, Up: Drag and Drop
+
+Drop Interface
+==============
+
+ For each activated low-level protocol, a internal routine will catch
+incoming drops and convert them to a dragdrop-drop type misc-user-event.
+
+ This misc-user-event has its function argument set to
+`dragdrop-drop-dispatch' and the object contains the data of the drop
+(converted to URL/MIME specific data). This function will search the
+variable `experimental-dragdrop-drop-functions' for a function that can
+handle the dropped data.
+
+ To modify the drop behavior, the user can modify the variable
+`experimental-dragdrop-drop-functions'. Each element of this list
+specifies a possible handler for dropped data. The first one that can
+handle the data will return `t' and exit. Another possibility is to set
+a extent-property with the same name. Extents are checked prior to the
+variable.
+
+ The customization group `drag-n-drop' shows all variables of user
+interest.
+
+\1f
+File: lispref.info, Node: Drag Interface, Prev: Drop Interface, Up: Drag and Drop
+
+Drag Interface
+==============
+
+ This describes the drag API (not implemented yet).
+
+\1f
+File: lispref.info, Node: Modes, Next: Documentation, Prev: Drag and Drop, Up: Top
+
+Major and Minor Modes
+*********************
+
+ A "mode" is a set of definitions that customize XEmacs and can be
+turned on and off while you edit. There are two varieties of modes:
+"major modes", which are mutually exclusive and used for editing
+particular kinds of text, and "minor modes", which provide features
+that users can enable individually.
+
+ This chapter describes how to write both major and minor modes, how
+to indicate them in the modeline, and how they run hooks supplied by the
+user. For related topics such as keymaps and syntax tables, see *Note
+Keymaps::, and *Note Syntax Tables::.
+
+* Menu:
+
+* Major Modes:: Defining major modes.
+* Minor Modes:: Defining minor modes.
+* Modeline Format:: Customizing the text that appears in the modeline.
+* Hooks:: How to use hooks; how to write code that provides hooks.
+
+\1f
+File: lispref.info, Node: Major Modes, Next: Minor Modes, Up: Modes
+
+Major Modes
+===========
+
+ Major modes specialize XEmacs for editing particular kinds of text.
+Each buffer has only one major mode at a time.
+
+ The least specialized major mode is called "Fundamental mode". This
+mode has no mode-specific definitions or variable settings, so each
+XEmacs command behaves in its default manner, and each option is in its
+default state. All other major modes redefine various keys and options.
+For example, Lisp Interaction mode provides special key bindings for
+<LFD> (`eval-print-last-sexp'), <TAB> (`lisp-indent-line'), and other
+keys.
+
+ When you need to write several editing commands to help you perform a
+specialized editing task, creating a new major mode is usually a good
+idea. In practice, writing a major mode is easy (in contrast to
+writing a minor mode, which is often difficult).
+
+ If the new mode is similar to an old one, it is often unwise to
+modify the old one to serve two purposes, since it may become harder to
+use and maintain. Instead, copy and rename an existing major mode
+definition and alter the copy--or define a "derived mode" (*note
+Derived Modes::). For example, Rmail Edit mode, which is in
+`emacs/lisp/rmailedit.el', is a major mode that is very similar to Text
+mode except that it provides three additional commands. Its definition
+is distinct from that of Text mode, but was derived from it.
+
+ Rmail Edit mode is an example of a case where one piece of text is
+put temporarily into a different major mode so it can be edited in a
+different way (with ordinary XEmacs commands rather than Rmail). In
+such cases, the temporary major mode usually has a command to switch
+back to the buffer's usual mode (Rmail mode, in this case). You might
+be tempted to present the temporary redefinitions inside a recursive
+edit and restore the usual ones when the user exits; but this is a bad
+idea because it constrains the user's options when it is done in more
+than one buffer: recursive edits must be exited most-recently-entered
+first. Using alternative major modes avoids this limitation. *Note
+Recursive Editing::.
+
+ The standard XEmacs Lisp library directory contains the code for
+several major modes, in files including `text-mode.el', `texinfo.el',
+`lisp-mode.el', `c-mode.el', and `rmail.el'. You can look at these
+libraries to see how modes are written. Text mode is perhaps the
+simplest major mode aside from Fundamental mode. Rmail mode is a
+complicated and specialized mode.
+
+* Menu:
+
+* Major Mode Conventions:: Coding conventions for keymaps, etc.
+* Example Major Modes:: Text mode and Lisp modes.
+* Auto Major Mode:: How XEmacs chooses the major mode automatically.
+* Mode Help:: Finding out how to use a mode.
+* Derived Modes:: Defining a new major mode based on another major
+ mode.
+
+\1f
+File: lispref.info, Node: Major Mode Conventions, Next: Example Major Modes, Up: Major Modes
+
+Major Mode Conventions
+----------------------
+
+ The code for existing major modes follows various coding conventions,
+including conventions for local keymap and syntax table initialization,
+global names, and hooks. Please follow these conventions when you
+define a new major mode:
+
+ * Define a command whose name ends in `-mode', with no arguments,
+ that switches to the new mode in the current buffer. This command
+ should set up the keymap, syntax table, and local variables in an
+ existing buffer without changing the buffer's text.
+
+ * Write a documentation string for this command that describes the
+ special commands available in this mode. `C-h m'
+ (`describe-mode') in your mode will display this string.
+
+ The documentation string may include the special documentation
+ substrings, `\[COMMAND]', `\{KEYMAP}', and `\<KEYMAP>', that
+ enable the documentation to adapt automatically to the user's own
+ key bindings. *Note Keys in Documentation::.
+
+ * The major mode command should start by calling
+ `kill-all-local-variables'. This is what gets rid of the local
+ variables of the major mode previously in effect.
+
+ * The major mode command should set the variable `major-mode' to the
+ major mode command symbol. This is how `describe-mode' discovers
+ which documentation to print.
+
+ * The major mode command should set the variable `mode-name' to the
+ "pretty" name of the mode, as a string. This appears in the mode
+ line.
+
+ * Since all global names are in the same name space, all the global
+ variables, constants, and functions that are part of the mode
+ should have names that start with the major mode name (or with an
+ abbreviation of it if the name is long). *Note Style Tips::.
+
+ * The major mode should usually have its own keymap, which is used
+ as the local keymap in all buffers in that mode. The major mode
+ function should call `use-local-map' to install this local map.
+ *Note Active Keymaps::, for more information.
+
+ This keymap should be kept in a global variable named
+ `MODENAME-mode-map'. Normally the library that defines the mode
+ sets this variable.
+
+ * The mode may have its own syntax table or may share one with other
+ related modes. If it has its own syntax table, it should store
+ this in a variable named `MODENAME-mode-syntax-table'. *Note
+ Syntax Tables::.
+
+ * The mode may have its own abbrev table or may share one with other
+ related modes. If it has its own abbrev table, it should store
+ this in a variable named `MODENAME-mode-abbrev-table'. *Note
+ Abbrev Tables::.
+
+ * Use `defvar' to set mode-related variables, so that they are not
+ reinitialized if they already have a value. (Such reinitialization
+ could discard customizations made by the user.)
+
+ * To make a buffer-local binding for an Emacs customization
+ variable, use `make-local-variable' in the major mode command, not
+ `make-variable-buffer-local'. The latter function would make the
+ variable local to every buffer in which it is subsequently set,
+ which would affect buffers that do not use this mode. It is
+ undesirable for a mode to have such global effects. *Note
+ Buffer-Local Variables::.
+
+ It's ok to use `make-variable-buffer-local', if you wish, for a
+ variable used only within a single Lisp package.
+
+ * Each major mode should have a "mode hook" named
+ `MODENAME-mode-hook'. The major mode command should run that
+ hook, with `run-hooks', as the very last thing it does. *Note
+ Hooks::.
+
+ * The major mode command may also run the hooks of some more basic
+ modes. For example, `indented-text-mode' runs `text-mode-hook' as
+ well as `indented-text-mode-hook'. It may run these other hooks
+ immediately before the mode's own hook (that is, after everything
+ else), or it may run them earlier.
+
+ * If something special should be done if the user switches a buffer
+ from this mode to any other major mode, the mode can set a local
+ value for `change-major-mode-hook'.
+
+ * If this mode is appropriate only for specially-prepared text, then
+ the major mode command symbol should have a property named
+ `mode-class' with value `special', put on as follows:
+
+ (put 'funny-mode 'mode-class 'special)
+
+ This tells XEmacs that new buffers created while the current
+ buffer has Funny mode should not inherit Funny mode. Modes such
+ as Dired, Rmail, and Buffer List use this feature.
+
+ * If you want to make the new mode the default for files with certain
+ recognizable names, add an element to `auto-mode-alist' to select
+ the mode for those file names. If you define the mode command to
+ autoload, you should add this element in the same file that calls
+ `autoload'. Otherwise, it is sufficient to add the element in the
+ file that contains the mode definition. *Note Auto Major Mode::.
+
+ * In the documentation, you should provide a sample `autoload' form
+ and an example of how to add to `auto-mode-alist', that users can
+ include in their `.emacs' files.
+
+ * The top-level forms in the file defining the mode should be
+ written so that they may be evaluated more than once without
+ adverse consequences. Even if you never load the file more than
+ once, someone else will.
+
+ - Variable: change-major-mode-hook
+ This normal hook is run by `kill-all-local-variables' before it
+ does anything else. This gives major modes a way to arrange for
+ something special to be done if the user switches to a different
+ major mode. For best results, make this variable buffer-local, so
+ that it will disappear after doing its job and will not interfere
+ with the subsequent major mode. *Note Hooks::.
+
+\1f
+File: lispref.info, Node: Example Major Modes, Next: Auto Major Mode, Prev: Major Mode Conventions, Up: Major Modes
+
+Major Mode Examples
+-------------------
+
+ Text mode is perhaps the simplest mode besides Fundamental mode.
+Here are excerpts from `text-mode.el' that illustrate many of the
+conventions listed above:
+
+ ;; Create mode-specific tables.
+ (defvar text-mode-syntax-table nil
+ "Syntax table used while in text mode.")
+
+ (if text-mode-syntax-table
+ () ; Do not change the table if it is already set up.
+ (setq text-mode-syntax-table (make-syntax-table))
+ (modify-syntax-entry ?\" ". " text-mode-syntax-table)
+ (modify-syntax-entry ?\\ ". " text-mode-syntax-table)
+ (modify-syntax-entry ?' "w " text-mode-syntax-table))
+
+ (defvar text-mode-abbrev-table nil
+ "Abbrev table used while in text mode.")
+ (define-abbrev-table 'text-mode-abbrev-table ())
+
+ (defvar text-mode-map nil) ; Create a mode-specific keymap.
+
+ (if text-mode-map
+ () ; Do not change the keymap if it is already set up.
+ (setq text-mode-map (make-sparse-keymap))
+ (define-key text-mode-map "\t" 'tab-to-tab-stop)
+ (define-key text-mode-map "\es" 'center-line)
+ (define-key text-mode-map "\eS" 'center-paragraph))
+
+ Here is the complete major mode function definition for Text mode:
+
+ (defun text-mode ()
+ "Major mode for editing text intended for humans to read.
+ Special commands: \\{text-mode-map}
+ Turning on text-mode runs the hook `text-mode-hook'."
+ (interactive)
+ (kill-all-local-variables)
+ (use-local-map text-mode-map) ; This provides the local keymap.
+ (setq mode-name "Text") ; This name goes into the modeline.
+ (setq major-mode 'text-mode) ; This is how `describe-mode'
+ ; finds the doc string to print.
+ (setq local-abbrev-table text-mode-abbrev-table)
+ (set-syntax-table text-mode-syntax-table)
+ (run-hooks 'text-mode-hook)) ; Finally, this permits the user to
+ ; customize the mode with a hook.
+
+ The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp
+Interaction mode) have more features than Text mode and the code is
+correspondingly more complicated. Here are excerpts from
+`lisp-mode.el' that illustrate how these modes are written.
+
+ ;; Create mode-specific table variables.
+ (defvar lisp-mode-syntax-table nil "")
+ (defvar emacs-lisp-mode-syntax-table nil "")
+ (defvar lisp-mode-abbrev-table nil "")
+
+ (if (not emacs-lisp-mode-syntax-table) ; Do not change the table
+ ; if it is already set.
+ (let ((i 0))
+ (setq emacs-lisp-mode-syntax-table (make-syntax-table))
+
+ ;; Set syntax of chars up to 0 to class of chars that are
+ ;; part of symbol names but not words.
+ ;; (The number 0 is `48' in the ASCII character set.)
+ (while (< i ?0)
+ (modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
+ (setq i (1+ i)))
+ ...
+ ;; Set the syntax for other characters.
+ (modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
+ (modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
+ ...
+ (modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
+ (modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
+ ...))
+ ;; Create an abbrev table for lisp-mode.
+ (define-abbrev-table 'lisp-mode-abbrev-table ())
+
+ Much code is shared among the three Lisp modes. The following
+function sets various variables; it is called by each of the major Lisp
+mode functions:
+
+ (defun lisp-mode-variables (lisp-syntax)
+ ;; The `lisp-syntax' argument is `nil' in Emacs Lisp mode,
+ ;; and `t' in the other two Lisp modes.
+ (cond (lisp-syntax
+ (if (not lisp-mode-syntax-table)
+ ;; The Emacs Lisp mode syntax table always exists, but
+ ;; the Lisp Mode syntax table is created the first time a
+ ;; mode that needs it is called. This is to save space.
+ (progn (setq lisp-mode-syntax-table
+ (copy-syntax-table emacs-lisp-mode-syntax-table))
+ ;; Change some entries for Lisp mode.
+ (modify-syntax-entry ?\| "\" "
+ lisp-mode-syntax-table)
+ (modify-syntax-entry ?\[ "_ "
+ lisp-mode-syntax-table)
+ (modify-syntax-entry ?\] "_ "
+ lisp-mode-syntax-table)))
+ (set-syntax-table lisp-mode-syntax-table)))
+ (setq local-abbrev-table lisp-mode-abbrev-table)
+ ...)
+
+ Functions such as `forward-paragraph' use the value of the
+`paragraph-start' variable. Since Lisp code is different from ordinary
+text, the `paragraph-start' variable needs to be set specially to
+handle Lisp. Also, comments are indented in a special fashion in Lisp
+and the Lisp modes need their own mode-specific
+`comment-indent-function'. The code to set these variables is the rest
+of `lisp-mode-variables'.
+
+ (make-local-variable 'paragraph-start)
+ ;; Having `^' is not clean, but `page-delimiter'
+ ;; has them too, and removing those is a pain.
+ (setq paragraph-start (concat "^$\\|" page-delimiter))
+ ...
+ (make-local-variable 'comment-indent-function)
+ (setq comment-indent-function 'lisp-comment-indent))
+
+ Each of the different Lisp modes has a slightly different keymap.
+For example, Lisp mode binds `C-c C-l' to `run-lisp', but the other
+Lisp modes do not. However, all Lisp modes have some commands in
+common. The following function adds these common commands to a given
+keymap.
+
+ (defun lisp-mode-commands (map)
+ (define-key map "\e\C-q" 'indent-sexp)
+ (define-key map "\177" 'backward-delete-char-untabify)
+ (define-key map "\t" 'lisp-indent-line))
+
+ Here is an example of using `lisp-mode-commands' to initialize a
+keymap, as part of the code for Emacs Lisp mode. First we declare a
+variable with `defvar' to hold the mode-specific keymap. When this
+`defvar' executes, it sets the variable to `nil' if it was void. Then
+we set up the keymap if the variable is `nil'.
+
+ This code avoids changing the keymap or the variable if it is already
+set up. This lets the user customize the keymap.
+
+ (defvar emacs-lisp-mode-map () "")
+ (if emacs-lisp-mode-map
+ ()
+ (setq emacs-lisp-mode-map (make-sparse-keymap))
+ (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun)
+ (lisp-mode-commands emacs-lisp-mode-map))
+
+ Finally, here is the complete major mode function definition for
+Emacs Lisp mode.
+
+ (defun emacs-lisp-mode ()
+ "Major mode for editing Lisp code to run in XEmacs.
+ Commands:
+ Delete converts tabs to spaces as it moves back.
+ Blank lines separate paragraphs. Semicolons start comments.
+ \\{emacs-lisp-mode-map}
+ Entry to this mode runs the hook `emacs-lisp-mode-hook'."
+ (interactive)
+ (kill-all-local-variables)
+ (use-local-map emacs-lisp-mode-map) ; This provides the local keymap.
+ (set-syntax-table emacs-lisp-mode-syntax-table)
+ (setq major-mode 'emacs-lisp-mode) ; This is how `describe-mode'
+ ; finds out what to describe.
+ (setq mode-name "Emacs-Lisp") ; This goes into the modeline.
+ (lisp-mode-variables nil) ; This defines various variables.
+ (run-hooks 'emacs-lisp-mode-hook)) ; This permits the user to use a
+ ; hook to customize the mode.
+
+\1f
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