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| -rw-r--r-- | lispref/text.texi | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/lispref/text.texi b/lispref/text.texi index 08723e5bc84..29e6c4fb3bd 100644 --- a/lispref/text.texi +++ b/lispref/text.texi @@ -986,6 +986,12 @@ Here's how you might undo the change: (put-text-property @var{beg} @var{end} @var{property} @var{value}) @end example +@item (@var{marker} . @var{adjustment}) +This kind of element records the fact that the marker @var{marker} was +relocated due to deletion of surrounding text, and that it moved +@var{adjustment} character positions. Undoing this element moves +@var{marker} @minus{} @var{adjustment} characters. + @item @var{position} This element indicates where point was at an earlier time. Undoing this element sets point to @var{position}. Deletion normally creates an @@ -2088,6 +2094,8 @@ along with the characters; this includes such diverse functions as neighboring text. * Saving Properties:: Saving text properties in files, and reading them back. +* Lazy Properties:: Computing text properties in a lazy fashion + only when text is examined. * Not Intervals:: Why text properties do not use Lisp-visible text intervals. @end menu @@ -2639,6 +2647,51 @@ types that are reasonably flexible, and not too hard to encode. @c ??? In next edition, merge this info Format Conversion. +@node Lazy Properties +@subsection Lazy Computation of Text Properties + + Instead of computing text properties for all the text in the buffer, +you can arrange to compute the text properties for parts of the text +when and if something depends on them. + + The primitive that extracts text from the buffer along with its +properties is @code{buffer-substring}. Before examining the properties, +this function runs the abnormal hook @code{buffer-access-fontify-functions}. + +@defvar buffer-access-fontify-functions +This variable holds a list of functions for computing text properties. +Before @code{buffer-substring} copies the text and text properties for a +portion of the buffer, it calls all the functions in this list. Each of +the functions receives two arguments that specify the range of the +buffer being accessed. (The buffer itself is always the current +buffer.) +@end defvar + + The function @code{buffer-substring-no-properties} does not call these +functions, since it ignores text properties anyway. + + In order to prevent the hook functions from being called more than +once for the same part of the buffer, you can use the variable +@code{buffer-access-fontified-property}. + +@defvar buffer-access-fontified-property +If this value's variable is non-@code{nil}, it is a symbol which is used +as a text property name. A non-@code{nil} value for that text property +means, ``the other text properties for this character have already been +computed.'' + +If all the characters in the range specified for @code{buffer-substring} +have a non-@code{nil} value for this property, @code{buffer-substring} +does not call the @code{buffer-access-fontify-functions} functions. It +assumes these characters already have the right text properties, and +just copies the properties they already have. + +The normal way to use this feature is that the +@code{buffer-access-fontify-functions} functions add this property, as +well as others, to the characters they operate on. That way, they avoid +being called over and over for the same text. +@end defvar + @node Not Intervals @subsection Why Text Properties are not Intervals @cindex intervals |