32.19.4 Properties with Special Meanings

Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like.

Note: the properties composition, display, invisible and intangible can also cause point to move to an acceptable place, after each Emacs command. See Adjusting Point.

category

If a character has a category property, we call it the property category of the character. It should be a symbol. The properties of this symbol serve as defaults for the properties of the character.

face

You can use the property face to control the font and color of text. See Faces, for more information.

In the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities;

• A face name (a symbol or string).
• A property list of face attributes. This has the form (keyword value ...), where each keyword is a face attribute name and value is a meaningful value for that attribute. With this feature, you do not need to create a face each time you want to specify a particular attribute for certain text. See Face Attributes.
• A cons cell with the form (foreground-color . color-name) or (background-color . color-name). These elements specify just the foreground color or just the background color. See Color Names, for the supported forms of color-name.

  A cons cell of (foreground-color . color-name) is equivalent to specifying (:foreground color-name); likewise for the background.

You can use Font Lock Mode (see Font Lock Mode), to dynamically update face properties based on the contents of the text.

font-lock-face

The font-lock-face property is the same in all respects as the face property, but its state of activation is controlled by font-lock-mode. This can be advantageous for special buffers which are not intended to be user-editable, or for static areas of text which are always fontified in the same way. See Precalculated Fontification.

Strictly speaking, font-lock-face is not a built-in text property; rather, it is implemented in Font Lock mode using char-property-alias-alist. See Examining Properties.

This property is new in Emacs 22.1.

mouse-face

The property mouse-face is used instead of face when the mouse is on or near the character. For this purpose, “near” means that all text between the character and where the mouse is have the same mouse-face property value.

fontified

This property says whether the text is ready for display. If nil, Emacs's redisplay routine calls the functions in fontification-functions (see Auto Faces) to prepare this part of the buffer before it is displayed. It is used internally by the “just in time” font locking code.

display

This property activates various features that change the way text is displayed. For example, it can make text appear taller or shorter, higher or lower, wider or narrow, or replaced with an image. See Display Property.

help-echo

If text has a string as its help-echo property, then when you move the mouse onto that text, Emacs displays that string in the echo area, or in the tooltip window (see Tooltips).

If the value of the help-echo property is a function, that function is called with three arguments, window, object and pos and should return a help string or nil for none. The first argument, window is the window in which the help was found. The second, object, is the buffer, overlay or string which had the help-echo property. The pos argument is as follows:

• If object is a buffer, pos is the position in the buffer.
• If object is an overlay, that overlay has a help-echo property, and pos is the position in the overlay's buffer.
• If object is a string (an overlay string or a string displayed with the display property), pos is the position in that string.

If the value of the help-echo property is neither a function nor a string, it is evaluated to obtain a help string.

You can alter the way help text is displayed by setting the variable show-help-function (see Help display).

This feature is used in the mode line and for other active text.

keymap

The keymap property specifies an additional keymap for commands. When this keymap applies, it is used for key lookup before the minor mode keymaps and before the buffer's local map. See Active Keymaps. If the property value is a symbol, the symbol's function definition is used as the keymap.

The property's value for the character before point applies if it is non-nil and rear-sticky, and the property's value for the character after point applies if it is non-nil and front-sticky. (For mouse clicks, the position of the click is used instead of the position of point.)

local-map

This property works like keymap except that it specifies a keymap to use instead of the buffer's local map. For most purposes (perhaps all purposes), it is better to use the keymap property.

syntax-table

The syntax-table property overrides what the syntax table says about this particular character. See Syntax Properties.

read-only

If a character has the property read-only, then modifying that character is not allowed. Any command that would do so gets an error, text-read-only. If the property value is a string, that string is used as the error message.

Insertion next to a read-only character is an error if inserting ordinary text there would inherit the read-only property due to stickiness. Thus, you can control permission to insert next to read-only text by controlling the stickiness. See Sticky Properties.

Since changing properties counts as modifying the buffer, it is not possible to remove a read-only property unless you know the special trick: bind inhibit-read-only to a non-nil value and then remove the property. See Read Only Buffers.

invisible

A non-nil invisible property can make a character invisible on the screen. See Invisible Text, for details.

intangible

If a group of consecutive characters have equal and non-nil intangible properties, then you cannot place point between them. If you try to move point forward into the group, point actually moves to the end of the group. If you try to move point backward into the group, point actually moves to the start of the group.

If consecutive characters have unequal non-nil intangible properties, they belong to separate groups; each group is separately treated as described above.

When the variable inhibit-point-motion-hooks is non-nil, the intangible property is ignored.

field

Consecutive characters with the same field property constitute a field. Some motion functions including forward-word and beginning-of-line stop moving at a field boundary. See Fields.

cursor

Normally, the cursor is displayed at the end of any overlay and text property strings present at the current window position. You can place the cursor on any desired character of these strings by giving that character a non-nil cursor text property.

pointer

This specifies a specific pointer shape when the mouse pointer is over this text or image. See Pointer Shape, for possible pointer shapes.

line-spacing

A newline can have a line-spacing text or overlay property that controls the height of the display line ending with that newline. The property value overrides the default frame line spacing and the buffer local line-spacing variable. See Line Height.

line-height

A newline can have a line-height text or overlay property that controls the total height of the display line ending in that newline. See Line Height.

modification-hooks

If a character has the property modification-hooks, then its value should be a list of functions; modifying that character calls all of those functions. Each function receives two arguments: the beginning and end of the part of the buffer being modified. Note that if a particular modification hook function appears on several characters being modified by a single primitive, you can't predict how many times the function will be called.

If these functions modify the buffer, they should bind inhibit-modification-hooks to t around doing so, to avoid confusing the internal mechanism that calls these hooks.

Overlays also support the modification-hooks property, but the details are somewhat different (see Overlay Properties).

insert-in-front-hooks

insert-behind-hooks

The operation of inserting text in a buffer also calls the functions listed in the insert-in-front-hooks property of the following character and in the insert-behind-hooks property of the preceding character. These functions receive two arguments, the beginning and end of the inserted text. The functions are called after the actual insertion takes place.

See also Change Hooks, for other hooks that are called when you change text in a buffer.

point-entered

point-left

The special properties point-entered and point-left record hook functions that report motion of point. Each time point moves, Emacs compares these two property values:

• the point-left property of the character after the old location, and
• the point-entered property of the character after the new location.

If these two values differ, each of them is called (if not nil) with two arguments: the old value of point, and the new one.

The same comparison is made for the characters before the old and new locations. The result may be to execute two point-left functions (which may be the same function) and/or two point-entered functions (which may be the same function). In any case, all the point-left functions are called first, followed by all the point-entered functions.

It is possible with char-after to examine characters at various buffer positions without moving point to those positions. Only an actual change in the value of point runs these hook functions.

— Variable: inhibit-point-motion-hooks

When this variable is non-nil, point-left and point-entered hooks are not run, and the intangible property has no effect. Do not set this variable globally; bind it with let.

— Variable: show-help-function

If this variable is non-nil, it specifies a function called to display help strings. These may be help-echo properties, menu help strings (see Simple Menu Items, see Extended Menu Items), or tool bar help strings (see Tool Bar). The specified function is called with one argument, the help string to display. Tooltip mode (see Tooltips) provides an example.

composition

This text property is used to display a sequence of characters as a single glyph composed from components. For instance, in Thai a base consonant is composed with the following combining vowel as a single glyph. The value should be a character or a sequence (vector, list, or string) of integers.

• If it is a character, it means to display that character instead of the text in the region.
• If it is a string, it means to display that string's contents instead of the text in the region.
• If it is a vector or list, the elements are characters interleaved with internal codes specifying how to compose the following character with the previous one.