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Minor improvement of documentation of '(when CONDITION . SPEC)'

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* doc/lispref/display.texi (Other Display Specs): Add a caveat
to using the '(when CONDITION . SPEC)' display specs.
This commit is contained in:
Eli Zaretskii 2019-03-04 19:49:47 +02:00
parent f872b65b2f
commit 52fd40068e
1 changed files with 10 additions and 0 deletions
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doc/lispref/display.texi
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@ -4853,6 +4853,16 @@ and the buffer position where the @code{display} property was found,
respectively. Both positions can be different when @code{object} is a
string.
Note that @var{condition} will only be evaluated when redisplay
examines the text where this display spec is located, so this feature
is best suited for conditions that are relatively stable, i.e.@:
yield, for each particular buffer position, the same results on every
evaluation. If the results change for the same text location, e.g.,
if the result depends on the position of point, then the conditional
specification might not do what you want, because redisplay examines
only those parts of buffer text where it has reasons to assume that
something changed since the last display cycle.
@node Display Margins
@subsection Displaying in the Margins
@cindex display margins