Meta Regex Engine

Given the pattern:

const1.complex1.const2.complex2…

that is a pattern that has at top level simple and complex pieces

Instead match this:

const1.*?const2.*?…

That is ignoring content of complex sub-expressions.

Then the validate step — run sub engines on each of the pieces requiring it to match the fulll exact slice.

2nd variation:

complex1.const1…

Here we handle the first one differently — match backwards from the start of const1.

This case is actually more important.