-- Searching with the Replace-Text MW-search-page.
-- Used Options shortcuts:
a) [Replace text in page contents]
b) [Replace text in page titles, when possible]
c) [Replace only in category]
These Options are displayed/presented to the user as seeming to be independent options.
Replace-Text behavior however shows that if option [a] is Off. All other option also 'seem' to be non-usable/-active.
For example:
With option [a] Off, but Option [b] On, and looking for "/doc" (templated"namespace) Replace-Text never finds anything.
Or:
If Option [c] is used (valid category specified), and option [a] is Off. A "/doc" search comes back with "No category exists with the name "Category:<used category>".
-- This seems more related to the fact that no matches where found.
For Replace-Text to provide less ambiguous UI-feedback to the user, based on this behavior, it kinda makes sense to auto-disable all options if [a] is Off.
... or to just lock Option [a] to On.
-- Not specific to any Replace-Text version.