bug#29222: 26.0.90; doc string of `search-invisible'

[Drew Adams]

This part of the doc string:

 When the value is 'open', if the text matched is made invisible by an
 overlay having an 'invisible' property and that overlay has a property
 'isearch-open-invisible', then incremental search will show the
 contents.

would be clearer if it said "an overlay having a non-nil 'invisible'
property" and "...has a non-nil property `isearch-open-invisible'.

Having a property is a bit ambiguous, or at least can be thought so.
Sure, it's true that one cannot tell the difference between not having
a property `foo' and having a property `foo' that has a value of nil.
Still, it's better to be explicit here, I think.



In GNU Emacs 26.0.90 (build 3, x86_64-w64-mingw32)
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