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#### 31.19.2 Changing Text Properties

The primitives for changing properties apply to a specified range of text in a buffer or string. The function `set-text-properties` (see end of section) sets the entire property list of the text in that range; more often, it is useful to add, change, or delete just certain properties specified by name.

Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (see Undo). Positions in a string start from 0, whereas positions in a buffer start from 1.

Function: put-text-property start end prop value &optional object

  This function sets the prop property to value for the text between start and end in the string or buffer object. If object is `nil`, it defaults to the current buffer.

Function: add-text-properties start end props &optional object

  This function adds or overrides text properties for the text between start and end in the string or buffer object. If object is `nil`, it defaults to the current buffer.

  The argument props specifies which properties to add. It should have the form of a property list (see Property Lists): a list whose elements include the property names followed alternately by the corresponding values.

  The return value is `t` if the function actually changed some property’s value; `nil` otherwise (if props is `nil` or its values agree with those in the text).

  For example, here is how to set the `comment` and `face` properties of a range of text:

      (add-text-properties start end
                           '(comment t face highlight))

Function: remove-text-properties start end props &optional object

  This function deletes specified text properties from the text between start and end in the string or buffer object. If object is `nil`, it defaults to the current buffer.

  The argument props specifies which properties to delete. It should have the form of a property list (see Property Lists): a list whose elements are property names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here’s how to remove the `face` property.

      (remove-text-properties start end '(face nil))

  The return value is `t` if the function actually changed some property’s value; `nil` otherwise (if props is `nil` or if no character in the specified text had any of those properties).

  To remove all text properties from certain text, use `set-text-properties` and specify `nil` for the new property list.

Function: remove-list-of-text-properties start end list-of-properties &optional object

  Like `remove-text-properties` except that list-of-properties is a list of property names only, not an alternating list of property names and values.

Function: set-text-properties start end props &optional object

  This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is `nil`, it defaults to the current buffer.

  The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.

  After `set-text-properties` returns, all the characters in the specified range have identical properties.

  If props is `nil`, the effect is to get rid of all properties from the specified range of text. Here’s an example:

      (set-text-properties start end nil)

  Do not rely on the return value of this function.

Function: add-face-text-property start end face &optional appendp object

  This function acts on the text between start and end, adding the face face to the `face` text property. face should be a valid value for the `face` property (see Special Properties), such as a face name or an anonymous face (see Faces).

  If any text in the region already has a non-`nil` `face` property, those face(s) are retained. This function sets the `face` property to a list of faces, with face as the first element (by default) and the pre-existing faces as the remaining elements. If the optional argument append is non-`nil`, face is appended to the end of the list instead. Note that in a face list, the first occurring value for each attribute takes precedence.

  For example, the following code would assign a italicized green face to the text between start and end:

      (add-face-text-property start end 'italic)
      (add-face-text-property start end '(:foreground "red"))
      (add-face-text-property start end '(:foreground "green"))

  The optional argument object, if non-`nil`, specifies a buffer or string to act on, rather than the current buffer. If object is a string, then start and end are zero-based indices into the string.

The easiest way to make a string with text properties is with `propertize`:

Function: propertize string &rest properties

  This function returns a copy of string with the text properties properties added. These properties apply to all the characters in the string that is returned. Here is an example that constructs a string with a `face` property and a `mouse-face` property:

      (propertize "foo" 'face 'italic
                  'mouse-face 'bold-italic)
           ⇒ #("foo" 0 3 (mouse-face bold-italic face italic))

  To put different properties on various parts of a string, you can construct each part with `propertize` and then combine them with `concat`:

      (concat
       (propertize "foo" 'face 'italic
                   'mouse-face 'bold-italic)
       " and "
       (propertize "bar" 'face 'italic
                   'mouse-face 'bold-italic))
           ⇒ #("foo and bar"
                       0 3 (face italic mouse-face bold-italic)
                       3 8 nil
                       8 11 (face italic mouse-face bold-italic))

See Buffer Contents, for the function `buffer-substring-no-properties`, which copies text from the buffer but does not copy its properties.

If you wish to add or remove text properties to a buffer without marking the buffer as modified, you can wrap the calls above in the `with-silent-modifications` macro.

Next: Property Search, Previous: Examining Properties, Up: Text Properties [Contents][Index]