

If you want to modify or add other characters to be considered as words, just go to Settings > Preferences.

And a word character represents any single letter, accentuated letter, digit or the _ character. If you prefer to search identical words, whatever their case, change the beginning of the regex from (?s-i) to (?si)īy default, the part \b(\w+)\b looks for the greatest range of word characters, between 2 non-word chars.

Here is a general solution which marks every word of File 1 ONLY IF this specific word is also present in File 2 :
