Consider regex as a separate flow

[mapto]

Regex makes sense to be used on single words (or a couple of words).
Depending on input, enable or disable it.
Also show equivalence table to user when they choose regex.
Possibly also let them modify it it.

To illustrate equivalence tables, for contemporary English, it could be something like:

u	ou
ize	ise

[mapto]

Regex makes sense for short matches, N-gram for long ones (when at least N tokens are present). So use them as alternatives to each other:

1. when not enough tokens in N-gram, use regex
2. when more than four whitespaces in regex, use 3-grams