This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2) v3.2, April, May 1997 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: lispref.info, Node: Creating and Modifying Extents, Next: Extent Endpoints, Prev: Intro to Extents, Up: Extents Creating and Modifying Extents ============================== - Function: make-extent FROM TO &optional OBJECT This function makes an extent for the range [FROM, TO) in OBJECT (a buffer or string). OBJECT defaults to the current buffer. Insertions at point TO will be outside of the extent; insertions at FROM will be inside the extent, causing the extent to grow (*note Extent Endpoints::.). This is the same way that markers behave. The extent is initially detached if both FROM and TO are `nil', and in this case OBJECT defaults to `nil', meaning the extent is in no buffer or string (*note Detached Extents::.). - Function: delete-extent EXTENT This function removes EXTENT from its buffer and destroys it. This does not modify the buffer's text, only its display properties. The extent cannot be used thereafter. To remove an extent in such a way that it can be re-inserted later, use `detach-extent'. *Note Detached Extents::. - Function: extent-object EXTENT This function returns the buffer or string that EXTENT is in. If the return value is `nil', this means that the extent is detached; however, a detached extent will not necessarily return a value of `nil'. - Function: extent-live-p EXTENT This function returns `nil' if EXTENT is deleted, and `t' otherwise.  File: lispref.info, Node: Extent Endpoints, Next: Finding Extents, Prev: Creating and Modifying Extents, Up: Extents Extent Endpoints ================ Every extent has a start position and an end position, and logically affects the characters between those positions. Normally the start and end positions must both be valid positions in the extent's buffer or string. However, both endpoints can be `nil', meaning the extent is detached. *Note Detached Extents::. Whether the extent overlaps its endpoints is governed by its `start-open' and `end-open' properties. Insertion of a character at a closed endpoint will expand the extent to include that character; insertion at an open endpoint will not. Similarly, functions such as `extent-at' that scan over all extents overlapping a particular position will include extents with a closed endpoint at that position, but not extents with an open endpoint. Note that the `start-closed' and `end-closed' properties are equivalent to `start-open' and `end-open' with the opposite sense. Both endpoints can be equal, in which case the extent includes no characters but still exists in the buffer or string. Zero-length extents are used to represent annotations (*note Annotations::.) and can be used as a more powerful form of a marker. Deletion of all the characters in an extent may or may not result in a zero-length extent; this depends on the `detachable' property (*note Detached Extents::.). Insertion at the position of a zero-length extent expands the extent if both endpoints are closed; goes before the extent if it has the `start-open' property; and goes after the extent if it has the `end-open' property. Zero-length extents with both the `start-open' and `end-open' properties are treated as if their starting point were closed. Deletion of a character on a side of a zero-length extent whose corresponding endpoint is closed causes the extent to be detached if its `detachable' property is set; if the corresponding endpoint is open, the extent remains in the buffer, moving as necessary. Extents are ordered within a buffer or string by increasing start position, and then by decreasing end position (this is called the "display order"). - Function: extent-start-position EXTENT This function returns the start position of EXTENT. - Function: extent-end-position EXTENT This function returns the end position of EXTENT. - Function: extent-length EXTENT This function returns the length of EXTENT in characters. If the extent is detached, this returns `0'. If the extent is not detached, this is equivalent to (- (extent-end-position EXTENT) (extent-start-position EXTENT)) - Function: set-extent-endpoints EXTENT START END &optional BUFFER-OR-STRING This function sets the start and end position of EXTENT to START and END. If both are `nil', this is equivalent to `detach-extent'. BUFFER-OR-STRING specifies the new buffer or string that the extent should be in, and defaults to EXTENT's buffer or string. (If `nil', and EXTENT is in no buffer and no string, it defaults to the current buffer.) See documentation on `detach-extent' for a discussion of undo recording.  File: lispref.info, Node: Finding Extents, Next: Mapping Over Extents, Prev: Extent Endpoints, Up: Extents Finding Extents =============== The following functions provide a simple way of determining the extents in a buffer or string. A number of more sophisticated primitives for mapping over the extents in a range of a buffer or string are also provided (*note Mapping Over Extents::.). When reading through this section, keep in mind the way that extents are ordered (*note Extent Endpoints::.). - Function: extent-list &optional BUFFER-OR-STRING FROM TO FLAGS This function returns a list of the extents in BUFFER-OR-STRING. BUFFER-OR-STRING defaults to the current buffer if omitted. FROM and TO can be used to limit the range over which extents are returned; if omitted, all extents in the buffer or string are returned. More specifically, if a range is specified using FROM and TO, only extents that overlap the range (i.e. begin or end inside of the range) are included in the list. FROM and TO default to the beginning and end of BUFFER-OR-STRING, respectively. FLAGS controls how end cases are treated. For a discussion of this, and exactly what "overlap" means, see `map-extents'. Functions that create extents must be prepared for the possibility that there are other extents in the same area, created by other functions. To deal with this, functions typically mark their own extents by setting a particular property on them. The following function makes it easier to locate those extents. - Function: extent-at POS &optional OBJECT PROPERTY BEFORE AT-FLAG This function finds the "smallest" extent (i.e., the last one in the display order) at (i.e., overlapping) POS in OBJECT (a buffer or string) having PROPERTY set. OBJECT defaults to the current buffer. PROPERTY defaults to `nil', meaning that any extent will do. Returns `nil' if there is no matching extent at POS. If the fourth argument BEFORE is not `nil', it must be an extent; any returned extent will precede that extent. This feature allows `extent-at' to be used by a loop over extents. AT-FLAG controls how end cases are handled (i.e. what "at" really means), and should be one of: `nil' `after' An extent is at POS if it covers the character after POS. This is consistent with the way that text properties work. `before' An extent is at POS if it covers the character before POS. `at' An extent is at POS if it overlaps or abuts POS. This includes all zero-length extents at POS. Note that in all cases, the start-openness and end-openness of the extents considered is ignored. If you want to pay attention to those properties, you should use `map-extents', which gives you more control. The following low-level functions are provided for explicitly traversing the extents in a buffer according to the display order. These functions are mostly intended for debugging - in normal operation, you should probably use `mapcar-extents' or `map-extents', or loop using the BEFORE argument to `extent-at', rather than creating a loop using `next-extent'. - Function: next-extent EXTENT Given an extent EXTENT, this function returns the next extent in the buffer or string's display order. If EXTENT is a buffer or string, this returns the first extent in the buffer or string. - Function: previous-extent EXTENT Given an extent EXTENT, this function returns the previous extent in the buffer or string's display order. If EXTENT is a buffer or string, this returns the last extent in the buffer or string.  File: lispref.info, Node: Mapping Over Extents, Next: Extent Properties, Prev: Finding Extents, Up: Extents Mapping Over Extents ==================== The most basic and general function for mapping over extents is called `map-extents'. You should read through the definition of this function to familiarize yourself with the concepts and optional arguments involved. However, in practice you may find it more convenient to use the function `mapcar-extents' or to create a loop using the `before' argument to `extent-at' (*note Finding Extents::.). - Function: map-extents FUNCTION &optional OBJECT FROM TO MAPARG FLAGS PROPERTY VALUE This function maps FUNCTION over the extents which overlap a region in OBJECT. OBJECT is normally a buffer or string but could be an extent (see below). The region is normally bounded by [FROM, TO) (i.e. the beginning of the region is closed and the end of the region is open), but this can be changed with the FLAGS argument (see below for a complete discussion). FUNCTION is called with the arguments (extent, MAPARG). The arguments OBJECT, FROM, TO, MAPARG, and FLAGS are all optional and default to the current buffer, the beginning of OBJECT, the end of OBJECT, NIL, and NIL, respectively. `map-extents' returns the first non-`nil' result produced by FUNCTION, and no more calls to FUNCTION are made after it returns non-`nil'. If OBJECT is an extent, FROM and TO default to the extent's endpoints, and the mapping omits that extent and its predecessors. This feature supports restarting a loop based on `map-extents'. Note: OBJECT must be attached to a buffer or string, and the mapping is done over that buffer or string. An extent overlaps the region if there is any point in the extent that is also in the region. (For the purpose of overlap, zero-length extents and regions are treated as closed on both ends regardless of their endpoints' specified open/closedness.) Note that the endpoints of an extent or region are considered to be in that extent or region if and only if the corresponding end is closed. For example, the extent [5,7] overlaps the region [2,5] because 5 is in both the extent and the region. However, (5,7] does not overlap [2,5] because 5 is not in the extent, and neither [5,7] nor (5,7] overlaps the region [2,5) because 5 is not in the region. The optional FLAGS can be a symbol or a list of one or more symbols, modifying the behavior of `map-extents'. Allowed symbols are: `end-closed' The region's end is closed. `start-open' The region's start is open. `all-extents-closed' Treat all extents as closed on both ends for the purpose of determining whether they overlap the region, irrespective of their actual open- or closedness. `all-extents-open' Treat all extents as open on both ends. `all-extents-closed-open' Treat all extents as start-closed, end-open. `all-extents-open-closed' Treat all extents as start-open, end-closed. `start-in-region' In addition to the above conditions for extent overlap, the extent's start position must lie within the specified region. Note that, for this condition, open start positions are treated as if 0.5 was added to the endpoint's value, and open end positions are treated as if 0.5 was subtracted from the endpoint's value. `end-in-region' The extent's end position must lie within the region. `start-and-end-in-region' Both the extent's start and end positions must lie within the region. `start-or-end-in-region' Either the extent's start or end position must lie within the region. `negate-in-region' The condition specified by a `*-in-region' flag must *not* hold for the extent to be considered. At most one of `all-extents-closed', `all-extents-open', `all-extents-closed-open', and `all-extents-open-closed' may be specified. At most one of `start-in-region', `end-in-region', `start-and-end-in-region', and `start-or-end-in-region' may be specified. If optional arg PROPERTY is non-`nil', only extents with that property set on them will be visited. If optional arg VALUE is non-`nil', only extents whose value for that property is `eq' to VALUE will be visited. If you want to map over extents and accumulate a list of results, the following function may be more convenient than `map-extents'. - Function: mapcar-extents FUNCTION &optional PREDICATE BUFFER-OR-STRING FROM TO FLAGS PROPERTY VALUE This function applies FUNCTION to all extents which overlap a region in BUFFER-OR-STRING. The region is delimited by FROM and TO. FUNCTION is called with one argument, the extent. A list of the values returned by FUNCTION is returned. An optional PREDICATE may be used to further limit the extents over which FUNCTION is mapped. The optional arguments FLAGS, PROPERTY, and VALUE may also be used to control the extents passed to PREDICATE or FUNCTION, and have the same meaning as in `map-extents'. - Function: map-extent-children FUNCTION &optional OBJECT FROM TO MAPARG FLAGS PROPERTY VALUE This function is similar to `map-extents', but differs in that: * It only visits extents which start in the given region. * After visiting an extent E, it skips all other extents which start inside E but end before E's end. Thus, this function may be used to walk a tree of extents in a buffer: (defun walk-extents (buffer &optional ignore) (map-extent-children 'walk-extents buffer)) - Function: extent-in-region-p EXTENT &optional FROM TO FLAGS This function returns T if `map-extents' would visit EXTENT if called with the given arguments.  File: lispref.info, Node: Extent Properties, Next: Detached Extents, Prev: Mapping Over Extents, Up: Extents Properties of Extents ===================== Each extent has a property list associating property names with values. Some property names have predefined meanings, and can usually only assume particular values. Assigning other values to such a property either cause the value to be converted into a legal value (e.g., assigning anything but `nil' to a Boolean property will cause the value of `t' to be assigned to the property) or will cause an error. Property names without predefined meanings can be assigned any value. An undefined property is equivalent to a property with a value of `nil', or with a particular default value in the case of properties with predefined meanings. Note that, when an extent is created, the `end-open' and `detachable' properties are set on it. If an extent has a parent, all of its properties actually derive from that parent (or from the root ancestor if the parent in turn has a parent), and setting a property of the extent actually sets that property on the parent. *Note Extent Parents::. - Function: extent-property EXTENT PROPERTY This function returns the value of PROPERTY in EXTENT. If PROPERTY is undefined, `nil' is returned. - Function: extent-properties EXTENT This function returns a list of all of EXTENT's properties that do not have the value of `nil' (or the default value, for properties with predefined meanings). - Function: set-extent-property EXTENT PROPERTY VALUE This function sets PROPERTY to VALUE in EXTENT. (If PROPERTY has a predefined meaning, only certain values are allowed, and some values may be converted to others before being stored.) - Function: set-extent-properties EXTENT PLIST Change some properties of EXTENT. PLIST is a property list. This is useful to change many extent properties at once. The following table lists the properties with predefined meanings, along with their allowable values. `detached' (Boolean) Whether the extent is detached. Setting this is the same as calling `detach-extent'. *Note Detached Extents::. `destroyed' (Boolean) Whether the extent has been deleted. Setting this is the same as calling `delete-extent'. `priority' (integer) The extent's redisplay priority. Defaults to 0. *Note priority: Intro to Extents. This property can also be set with `set-extent-priority' and accessed with `extent-priority'. `start-open' (Boolean) Whether the start position of the extent is open, meaning that characters inserted at that position go outside of the extent. *Note Extent Endpoints::. `start-closed' (Boolean) Same as `start-open' but with the opposite sense. Setting this property clears `start-open' and vice-versa. `end-open' (Boolean) Whether the end position of the extent is open, meaning that characters inserted at that position go outside of the extent. This is `t' by default. *Note Extent Endpoints::. `end-closed' (Boolean) Same as `end-open' but with the opposite sense. Setting this property clears `end-open' and vice-versa. `read-only' (Boolean) Whether text within this extent will be unmodifiable. `face' (face, face name, list of faces or face names, or `nil') The face in which to display the extent's text. This property can also be set with `set-extent-face' and accessed with `extent-face'. Note that if a list of faces is specified, the faces are merged together, with faces earlier in the list having priority over faces later in the list. `mouse-face' (face, face name, list of faces or face names, or `nil') The face used to display the extent when the mouse moves over it. This property can also be set with `set-extent-mouse-face' and accessed with `extent-mouse-face'. Note that if a list of faces is specified, the faces are merged together, with faces earlier in the list having priority over faces later in the list. *Note Extents and Events::. `pointer' (pointer glyph) The glyph used as the pointer when the mouse moves over the extent. This takes precedence over the `text-pointer-glyph' and `nontext-pointer-glyph' variables. If for any reason this glyph is an invalid pointer, the standard glyphs will be used as fallbacks. *Note Mouse Pointer:: `detachable' (Boolean) Whether this extent becomes detached when all of the text it covers is deleted. This is `t' by default. *Note Detached Extents::. `duplicable' (Boolean) Whether this extent should be copied into strings, so that kill, yank, and undo commands will restore or copy it. *Note Duplicable Extents::. `unique' (Boolean) Meaningful only in conjunction with `duplicable'. When this is set, there may be only one instance of this extent attached at a time. *Note Duplicable Extents::. `invisible' (Boolean) If `t', text under this extent will not be displayed - it will look as if the text is not there at all. `keymap' (keymap or `nil') This keymap is consulted for mouse clicks on this extent or keypresses made while `point' is within the extent. *Note Extents and Events::. `copy-function' This is a hook that is run when a duplicable extent is about to be copied from a buffer to a string (or the kill ring). *Note Duplicable Extents::. `paste-function' This is a hook that is run when a duplicable extent is about to be copied from a string (or the kill ring) into a buffer. *Note Duplicable Extents::. `begin-glyph' (glyph or `nil') This extent's begin glyph. *Note Annotations::. `end-glyph' (glyph or `nil') This extent's end glyph. *Note Annotations::. `begin-glyph-layout' (`text', `whitespace', `inside-margin', or `outside-margin') The layout policy for this extent's begin glyph. Defaults to `text'. *Note Annotations::. `end-glyph-layout' (`text', `whitespace', `inside-margin', or `outside-margin') The layout policy for this extent's end glyph. Defaults to `text'. *Note Annotations::. `initial-redisplay-function' (any funcallable object) The function to be called the first time (a part of) the extent is redisplayed. It will be called with the extent as its argument. This is used by `lazy-shot' to implement lazy font-locking. The functionality is still experimental, and may change without further notice. The following convenience functions are provided for accessing particular properties of an extent. - Function: extent-face EXTENT This function returns the `face' property of EXTENT. This might also return a list of face names. Do not modify this list directly! Instead, use `set-extent-face'. Note that you can use `eq' to compare lists of faces as returned by `extent-face'. In other words, if you set the face of two different extents to two lists that are `equal' but not `eq', then the return value of `extent-face' on the two extents will return the identical list. - Function: extent-mouse-face EXTENT This function returns the `mouse-face' property of EXTENT. This might also return a list of face names. Do not modify this list directly! Instead, use `set-extent-mouse-face'. Note that you can use `eq' to compare lists of faces as returned by `extent-mouse-face', just like for `extent-face'. - Function: extent-priority EXTENT This function returns the `priority' property of EXTENT. - Function: extent-keymap EXTENT This function returns the `keymap' property of EXTENT. - Function: extent-begin-glyph-layout EXTENT This function returns the `begin-glyph-layout' property of EXTENT, i.e. the layout policy associated with the EXTENT's begin glyph. - Function: extent-end-glyph-layout EXTENT This function returns the `end-glyph-layout' property of EXTENT, i.e. the layout policy associated with the EXTENT's end glyph. - Function: extent-begin-glyph EXTENT This function returns the `begin-glyph' property of EXTENT, i.e. the glyph object displayed at the beginning of EXTENT. If there is none, `nil' is returned. - Function: extent-end-glyph EXTENT This function returns the `end-glyph' property of EXTENT, i.e. the glyph object displayed at the end of EXTENT. If there is none, `nil' is returned. The following convenience functions are provided for setting particular properties of an extent. - Function: set-extent-priority EXTENT PRI This function sets the `priority' property of EXTENT to PRI. - Function: set-extent-face EXTENT FACE This function sets the `face' property of EXTENT to FACE. - Function: set-extent-mouse-face EXTENT FACE This function sets the `mouse-face' property of EXTENT to FACE. - Function: set-extent-keymap EXTENT KEYMAP This function sets the `keymap' property of EXTENT to KEYMAP. KEYMAP must be either a keymap object, or `nil'. - Function: set-extent-begin-glyph-layout EXTENT LAYOUT This function sets the `begin-glyph-layout' property of EXTENT to LAYOUT. - Function: set-extent-end-glyph-layout EXTENT LAYOUT This function sets the `end-glyph-layout' property of EXTENT to LAYOUT. - Function: set-extent-begin-glyph EXTENT BEGIN-GLYPH &optional LAYOUT This function sets the `begin-glyph' and `glyph-layout' properties of EXTENT to BEGIN-GLYPH and LAYOUT, respectively. (LAYOUT defaults to `text' if not specified.) - Function: set-extent-end-glyph EXTENT END-GLYPH &optional LAYOUT This function sets the `end-glyph' and `glyph-layout' properties of EXTENT to END-GLYPH and LAYOUT, respectively. (LAYOUT defaults to `text' if not specified.) - Function: set-extent-initial-redisplay-function EXTENT FUNCTION This function sets the `initial-redisplay-function' property of the extent to FUNCTION.  File: lispref.info, Node: Detached Extents, Next: Extent Parents, Prev: Extent Properties, Up: Extents Detached Extents ================ A detached extent is an extent that is not attached to a buffer or string but can be re-inserted. Detached extents have a start position and end position of `nil'. Extents can be explicitly detached using `detach-extent'. An extent is also detached when all of its characters are all killed by a deletion, if its `detachable' property is set; if this property is not set, the extent becomes a zero-length extent. (Zero-length extents with the `detachable' property set behave specially. *Note zero-length extents: Extent Endpoints.) - Function: detach-extent EXTENT This function detaches EXTENT from its buffer or string. If EXTENT has the `duplicable' property, its detachment is tracked by the undo mechanism. *Note Duplicable Extents::. - Function: extent-detached-p EXTENT This function returns `nil' if EXTENT is detached, and `t' otherwise. - Function: copy-extent EXTENT &optional OBJECT This function makes a copy of EXTENT. It is initially detached. Optional argument OBJECT defaults to EXTENT's object (normally a buffer or string, but could be `nil'). - Function: insert-extent EXTENT &optional START END NO-HOOKS OBJECT This function inserts EXTENT from START to END in OBJECT (a buffer or string). If EXTENT is detached from a different buffer or string, or in most cases when EXTENT is already attached, the extent will first be copied as if with `copy-extent'. This function operates the same as if `insert' were called on a string whose extent data calls for EXTENT to be inserted, except that if NO-HOOKS is non-`nil', EXTENT's `paste-function' will not be invoked. *Note Duplicable Extents::.  File: lispref.info, Node: Extent Parents, Next: Duplicable Extents, Prev: Detached Extents, Up: Extents Extent Parents ============== An extent can have a parent extent set for it. If this is the case, the extent derives all its properties from that extent and has no properties of its own. The only "properties" that the extent keeps are the buffer or string it refers to and the start and end points. (More correctly, the extent's own properties are shadowed. If you later change the extent to have no parent, its own properties will become visible again.) It is possible for an extent's parent to itself have a parent, and so on. Through this, a whole tree of extents can be created, all deriving their properties from one root extent. Note, however, that you cannot create an inheritance loop - this is explicitly disallowed. Parent extents are used to implement the extents over the modeline. - Function: set-extent-parent EXTENT PARENT This function sets the parent of EXTENT to PARENT. If PARENT is `nil', the extent is set to have no parent. - Function: extent-parent EXTENT This function return the parents (if any) of EXTENT, or `nil'. - Function: extent-children EXTENT This function returns a list of the children (if any) of EXTENT. The children of an extent are all those extents whose parent is that extent. This function does not recursively trace children of children. - Function: extent-descendants EXTENT This function returns a list of all descendants of EXTENT, including EXTENT. This recursively applies `extent-children' to any children of EXTENT, until no more children can be found.  File: lispref.info, Node: Duplicable Extents, Next: Extents and Events, Prev: Extent Parents, Up: Extents Duplicable Extents ================== If an extent has the `duplicable' property, it will be copied into strings, so that kill, yank, and undo commands will restore or copy it. Specifically: * When a string is created using `buffer-substring' or `buffer-string', any duplicable extents in the region corresponding to the string will be copied into the string (*note Buffer Contents::.). When the string in inserted into a buffer using `insert', `insert-before-markers', `insert-buffer' or `insert-buffer-substring', the extents in the string will be copied back into the buffer (*note Insertion::.). The extents in a string can, of course, be retrieved explicitly using the standard extent primitives over the string. * Similarly, when text is copied or cut into the kill ring, any duplicable extents will be remembered and reinserted later when the text is pasted back into a buffer. * When `concat' is called on strings, the extents in the strings are copied into the resulting string. * When `substring' is called on a string, the relevant extents are copied into the resulting string. * When a duplicable extent is detached by `detach-extent' or string deletion, or inserted by `insert-extent' or string insertion, the action is recorded by the undo mechanism so that it can be undone later. Note that if an extent gets detached and then a later undo causes the extent to get reinserted, the new extent will not be `eq' to the original extent. * Extent motion, face changes, and attachment via `make-extent' are not recorded by the undo mechanism. This means that extent changes which are to be undo-able must be performed by character editing, or by insertion and detachment of duplicable extents. * A duplicable extent's `copy-function' property, if non-`nil', should be a function, and will be run when a duplicable extent is about to be copied from a buffer to a string (or the kill ring). It is called with three arguments: the extent and the buffer positions within it which are being copied. If this function returns `nil', then the extent will not be copied; otherwise it will. * A duplicable extent's `paste-function' property, if non-`nil', should be a function, and will be run when a duplicable extent is about to be copied from a string (or the kill ring) into a buffer. It is called with three arguments: the original extent and the buffer positions which the copied extent will occupy. (This hook is run after the corresponding text has already been inserted into the buffer.) Note that the extent argument may be detached when this function is run. If this function returns `nil', no extent will be inserted. Otherwise, there will be an extent covering the range in question. Note: if the extent to be copied is already attached to the buffer and overlaps the new range, the extent will simply be extended and the `paste-function' will not be called.  File: lispref.info, Node: Extents and Events, Next: Atomic Extents, Prev: Duplicable Extents, Up: Extents Interaction of Extents with Keyboard and Mouse Events ===================================================== If an extent has the `mouse-face' property set, it will be highlighted when the mouse passes over it. Highlighting is accomplished by merging the extent's face with the face or faces specified by the `mouse-face' property. The effect is as if a pseudo-extent with the `mouse-face' face were inserted after the extent in the display order (*note Extent Endpoints::., display order). - Variable: mouse-highlight-priority This variable holds the priority to use when merging in the highlighting pseudo-extent. The default is 1000. This is purposely set very high so that the highlighting pseudo-extent shows up even if there are other extents with various priorities at the same location. You can also explicitly cause an extent to be highlighted. Only one extent at a time can be highlighted in this fashion, and any other highlighted extent will be de-highlighted. - Function: highlight-extent EXTENT &optional HIGHLIGHT-P This function highlights (if HIGHLIGHT-P is non-`nil') or de-highlights (if HIGHLIGHT-P is `nil') EXTENT, if EXTENT has the `mouse-face' property. (Nothing happens if EXTENT does not have the `mouse-face' property.) - Function: force-highlight-extent EXTENT &optional HIGHLIGHT-P This function is similar to `highlight-extent' but highlights or de-highlights the extent regardless of whether it has the `mouse-face' property. If an extent has a `keymap' property, this keymap will be consulted for mouse clicks on the extent and keypresses made while `point' is within the extent. The behavior of mouse clicks and keystrokes not defined in the keymap is as normal for the buffer.  File: lispref.info, Node: Atomic Extents, Prev: Extents and Events, Up: Extents Atomic Extents ============== If the Lisp file `atomic-extents' is loaded, then the atomic extent facility is available. An "atomic extent" is an extent for which `point' cannot be positioned anywhere within it. This ensures that when selecting text, either all or none of the extent is selected. To make an extent atomic, set its `atomic' property.  File: lispref.info, Node: Specifiers, Next: Faces and Window-System Objects, Prev: Extents, Up: Top Specifiers ********** A specifier is an object used to keep track of a property whose value may vary depending on the particular situation (e.g. particular buffer displayed in a particular window) that it is used in. The value of many built-in properties, such as the font, foreground, background, and such properties of a face and variables such as `modeline-shadow-thickness' and `top-toolbar-height', is actually a specifier object. The specifier object, in turn, is "instanced" in a particular situation to yield the real value of the property in that situation. - Function: specifierp OBJECT This function returns non-`nil' if OBJECT is a specifier. * Menu: * Introduction to Specifiers:: Specifiers provide a clean way for display and other properties to vary (under user control) in a wide variety of contexts. * Specifiers In-Depth:: Gory details about specifier innards. * Specifier Instancing:: Instancing means obtaining the "value" of a specifier in a particular context. * Specifier Types:: Specifiers come in different flavors. * Adding Specifications:: Specifications control a specifier's "value" by giving conditions under which a particular value is valid. * Retrieving Specifications:: Querying a specifier's specifications. * Specifier Tag Functions:: Working with specifier tags. * Specifier Instancing Functions:: Functions to instance a specifier. * Specifier Example:: Making all this stuff clearer. * Creating Specifiers:: Creating specifiers for your own use. * Specifier Validation Functions:: Validating the components of a specifier. * Other Specification Functions:: Other ways of working with specifications.  File: lispref.info, Node: Introduction to Specifiers, Next: Specifiers In-Depth, Up: Specifiers Introduction to Specifiers ========================== Sometimes you may want the value of a property to vary depending on the context the property is used in. A simple example of this in XEmacs is buffer-local variables. For example, the variable `modeline-format', which controls the format of the modeline, can have different values depending on the particular buffer being edited. The variable has a default value which most modes will use, but a specialized package such as Calendar might change the variable so as to tailor the modeline to its own purposes. Other properties (such as those that can be changed by the `modify-frame-parameters' function, for example the color of the text cursor) can have frame-local values, although it might also make sense for them to have buffer-local values. In other cases, you might want the property to vary depending on the particular window within the frame that applies (e.g. the top or bottom window in a split frame), the device type that that frame appears on (X or tty), etc. Perhaps you can envision some more complicated scenario where you want a particular value in a specified buffer, another value in all other buffers displayed on a particular frame, another value in all other buffers displayed in all other frames on any mono (two-color, e.g. black and white only) displays, and a default value in all other circumstances. A "specifier" is a generalization of this, allowing a great deal of flexibility in controlling exactly what value a property has in which circumstances. It is most commonly used for display properties, such as an image or the foreground color of a face. As a simple example, you can specify that the foreground of the default face be * blue for a particular buffer * green for all other buffers As a more complicated example, you could specify that the foreground of the default face be * forest green for all buffers displayed in a particular Emacs window, or green if the X server doesn't recognize the color `forest green' * blue for all buffers displayed in a particular frame * red for all other buffers displayed on a color device * white for all other buffers  File: lispref.info, Node: Specifiers In-Depth, Next: Specifier Instancing, Prev: Introduction to Specifiers, Up: Specifiers In-Depth Overview of a Specifier ================================ A specifier object encapsulates a set of "specifications", each of which says what its value should be if a particular condition applies. For example, one specification might be "The value should be darkseagreen2 on X devices" another might be "The value should be blue in the *Help* buffer". In specifier terminology, these conditions are called "locales" and the values are called "instantiators". Given a specifier, a logical question is "What is its value in a particular situation?" This involves looking through the specifications to see which ones apply to this particular situation, and perhaps preferring one over another if more than one applies. In specifier terminology, a "particular situation" is called a "domain", and determining its value in a particular domain is called "instancing". Most of the time, a domain is identified by a particular window. For example, if the redisplay engine is drawing text in the default face in a particular window, it retrieves the specifier for the foreground color of the default face and "instances" it in the domain given by that window; in other words, it asks the specifier, "What is your value in this window?". More specifically, a specifier contains a set of "specifications", each of which associates a "locale" (a buffer object, a window object, a frame object, a device object, or the symbol `global') with an "inst-list", which is a list of one or more "inst-pairs". (For each possible locale, there can be at most one specification containing that locale.) Each inst-pair is a cons of a "tag set" (an unordered list of zero or more symbols, or "tags") and an "instantiator" (the allowed form of this varies depending on the type of specifier). In a given specification, there may be more than one inst-pair with the same tag set; this is unlike for locales. The tag set is used to restrict the sorts of devices over which the instantiator is valid and to uniquely identify instantiators added by a particular application, so that different applications can work on the same specifier and not interfere with each other. Each tag can have a "predicate" associated with it, which is a function of one argument (a device) that specifies whether the tag matches that particular device. (If a tag does not have a predicate, it matches all devices.) All tags in a tag set must match a device for the associated inst-pair to be instantiable over that device. (A null tag set is perfectly valid.) The valid device types (normally `x', `tty', and `stream') and device classes (normally `color', `grayscale', and `mono') can always be used as tags, and match devices of the associated type or class (*note Consoles and Devices::.). User-defined tags may be defined, with an optional predicate specified. An application can create its own tag, use it to mark all its instantiators, and be fairly confident that it will not interfere with other applications that modify the same specifier - Functions that add a specification to a specifier usually only overwrite existing inst-pairs with the same tag set as was given, and a particular tag or tag set can be specified when removing instantiators. When a specifier is instanced in a domain, both the locale and the tag set can be viewed as specifying necessary conditions that must apply in that domain for an instantiator to be considered as a possible result of the instancing. More specific locales always override more general locales (thus, there is no particular ordering of the specifications in a specifier); however, the tag sets are simply considered in the order that the inst-pairs occur in the specification's inst-list. Note also that the actual object that results from the instancing (called an "instance object") may not be the same as the instantiator from which it was derived. For some specifier types (such as integer specifiers and boolean specifiers), the instantiator will be returned directly as the instance object. For other types, however, this is not the case. For example, for font specifiers, the instantiator is a font-description string and the instance object is a font-instance object, which describes how the font is displayed on a particular device. A font-instance object encapsulates such things as the actual font name used to display the font on that device (a font-description string under X is usually a wildcard specification that may resolve to different font names, with possibly different foundries, widths, etc., on different devices), the extra properties of that font on that device, etc. Furthermore, this conversion (called "instantiation") might fail - a font or color might not exist on a particular device, for example.  File: lispref.info, Node: Specifier Instancing, Next: Specifier Types, Prev: Specifiers In-Depth, Up: Specifiers How a Specifier Is Instanced ============================ Instancing of a specifier in a particular window domain proceeds as follows: * First, XEmacs searches for a specification whose locale is the same as the window's buffer. If that fails, the search is repeated, looking for a locale that is the same as the window itself. If that fails, the search is repeated using the window's frame, then using the device that frame is on. Finally, the specification whose locale is the symbol `global' (if there is such a specification) is considered. * The inst-pairs contained in the specification that was found are considered in their order in the inst-list, looking for one whose tag set matches the device that is derived from the window domain. (The tag set is an unordered list of zero or more tag symbols. For all tags that have predicates associated with them, the predicate must match the device.) * If a matching tag set is found, the corresponding instantiator is passed to the specifier's instantiation method, which is specific to the type of the specifier. If it succeeds, the resulting instance object is returned as the result of the instancing and the instancing is done. Otherwise, the operation continues, looking for another matching inst-pair in the current specification. * When there are no more inst-pairs to be considered in the current specification, the search starts over, looking for another specification as in the first step above. * If all specifications are exhausted and no instance object can be derived, the instancing fails. (Actually, this is not completely true. Some specifier objects for built-in properties have a "fallback" value, which is either an inst-list or another specifier object, that is consulted if the instancing is about to fail. If it is an inst-list, the searching proceeds using the inst-pairs in that list. If it is a specifier, the entire instancing starts over using that specifier instead of the given one. Fallback values are set by the C code and cannot be modified, except perhaps indirectly, using any Lisp functions. The purpose of them is to supply some values to make sure that instancing of built-in properties can't fail and to implement some basic specifier inheritance, such as the fact that faces inherit their properties from the `default' face.) It is also possible to instance a specifier over a frame domain or device domain instead of over a window domain. The C code, for example, instances the `top-toolbar-height' variable over a frame domain in order to determine the height of a frame's top toolbar. Instancing over a frame or device is similar to instancing over a window except that specifications for locales that cannot be derived from the domain are ignored. Specifically, instancing over a frame looks first for frame locales, then device locales, then the `global' locale. Instancing over a device domain looks only for device locales and the `global' locale.