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(Display Property): Explain the significance

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of having text properties that are eq.
(Other Display Specs): Explain string as display spec.
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Richard M. Stallman 2005-03-17 23:19:40 +00:00
parent 9644814c81
commit 4db6da64fb
1 changed files with 52 additions and 1 deletions
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53
lispref/display.texi
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@ -3064,7 +3064,55 @@ buffer. The default is to use the @code{arrow} (non-text) pointer.
insert images into text, and also control other aspects of how text
displays. The value of the @code{display} property should be a
display specification, or a list or vector containing several display
specifications. The rest of this section describes several kinds of
specifications.
Some kinds of @code{display} properties specify something to display
instead of the text that has the property. In this case, ``the text''
means all the consecutive characters that have the same Lisp object as
their @code{display} property; these characters are replaced as a
single unit. By contrast, characters that have similar but distinct
Lisp objects as their @code{display} properties are handled
separately. Here's a function that illustrates this point:
@example
(defun foo ()
(goto-char (point-min))
(dotimes (i 5)
(let ((string (concat "A")))
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 1)
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 1))))
@end example
@noindent
It gives each of the first ten characters in the buffer string
@code{"A"} as the @code{display} property, but they don't all get the
same string. The first two characters get the same string, so they
together are replaced with one @samp{A}. The next two characters get
a second string, so they together are replaced with one @samp{A}.
Likewise for each following pair of characters. Thus, the ten
characters appear as five A's. This function would have the same
results:
@example
(defun foo ()
(goto-char (point-min))
(dotimes (i 5)
(let ((string (concat "A")))
(put-text-property (point) (2+ (point)) 'display string)
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 2))))
@end example
@noindent
This illustrates that what matters is the property value for
each character. If two consecutive characters have the same
object as the @code{display} property value, it's irrelevent
whether they got this property from a single call to
@code{put-text-property} or from two different calls.
The rest of this section describes several kinds of
display specifications and what they mean.
@menu
@ -3216,6 +3264,9 @@ the value of the expressions.
in the @code{display} text property.
@table @code
@item @var{string}
Display @var{string} instead of the text that has this property.
@item (image . @var{image-props})
This display specification is an image descriptor (@pxref{Images}).
When used as a display specification, it means to display the image