isearch-filter-predicate

isearch-filter-predicate is a variable defined in `isearch.el'.
Its value is

isearch-filter-visible

• This variable may be risky if used as a file-local variable.

Documentation:
Predicate that filters the search hits that would normally be available.
Search hits that dissatisfy the predicate are skipped. The function
has two arguments: the positions of start and end of text matched by
the search. If this function returns nil, continue searching without
stopping at this match.
If you use `add-function' to modify this variable, you can use the
`isearch-message-prefix' advice property to specify the prefix string
displayed in the search message.