Scope of backtracking for chunk manipulation purposes?

[bmeck]

for a given set of text manipulating chunks: a and b and a pattern p:

// any <br> following another <br>
let p = /(?<=<br>)<br>/
let a = ''
let b = '<br>'

Match results from b would change if a changed to <br>. When matching just b individually it would be good to know if it backtracked to the start of b for lookbehind not just if it reached the end of b.

This is a slight oddity due to less ecosystem data on lookbehind. This could be in or out of scope depending.

[bmeck]

I'd note opaque boundaries in Java using useTransparentBounds do allow this and and some other things like PCRE2_INFO_MAXLOOKBEHIND allow this to some extent.