Thanks for this, I had something like trigrams in mind.

But for full automatic regex support one would need to analyse the regex and identify the substrings which are in all execution paths ...

Quite a task.

Though... Perl does some optimisation when compiling its regexes and it's possible to introspect the result. It might be possible to build on this.

On a side note: true, the index adds 150% to the datas size. But the speed gain is dramatic enough to justify it in many use cases.