The search is based on Perl-compatible, case-insensitive regular expressions. Thus:

1. If you want to look for a sequence of characters, simply type the sequence.
2. If you want to look for a word, type \byour-word\b, with the backslashes.
3. If the word is the only word on its line, type ^your-word$
4. If you only have a part of a word, type that part.
5. If you want to look for characters separated by arbitrary characters, type .* (a dot and a star, no spaces between and at either end) in the search field between your words

Additionally, \d means [0-9], \w means [a-zA-z0-9_], \s - whitespace, \b - word border.
More details on Perl pages.

Patterns matching any word (such as .*, all periods etc.) are forbidden. The expression should be at least two characters long.