Doing Edit|Find&Replace to search for text in a Writer document doesn't search
in text marked as hidden.  This is true even if the text is conditionally unhidden.

At the top of a test document, do Insert|Fields|Other|Variables.  Select 'Set
variable' and enter a name of TEST and value of 0.  Then add some regular text
to the document.  Then insert some conditionally hidden text.
Insert|Fields|Other|Functions.  Then select 'Hidden text'.  Set Condition to
TEST and 'Hidden text' to "foo".  You should see "foo" in the document text
because the condition evaluates to false so it is NOT hidden.

Now bring up Find&Replace, enter "foo" and press Find.  It won't find the text
in the hidden (but visible) text.

I use hidden text and hidden sections in a single source document to produce
version-specific software documentation.  I conditionally hide text for some
versions when printing the document, but always leave the text visible when
editing it.  If I need to search and replace a term, there's no way for me to
find the many instances of the term when it appears in the conditionally hidden
text.

Note that find works with text in conditionally hidden sections.