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 (Note:Undo).
- 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 (Note: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 (Note: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: 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)
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 which has the text
properties PROPERTIES. 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 also the function `buffer-substring-no-properties' (Note:Buffer
Contents) which copies text from the buffer but does not copy its
properties.