I dunno about the live-regex/Incremental search for “In Files”
But XNews.exe has a very useful tool built-in, “Test Regex”
Pattern: (Regex Pattern).*(goes here).?
Test String: Example string for Regex Pattern to match goes here.
Matched String and sub-expressions:
00) Regex Pattern to match goes here.
01) Regex Pattern
02) goes here
The dialog has a [Match] and [Close] button, and a [x] Match case, checkbox.