> The core idea is to use a recursive descent parser to build an abstract syntax tree (AST) that describes the structure of all bracket pairs.

This is a really nice and clear blog post on an algorithmic challenge wonderfully addressed to a satisfactory conclusion (the rebalancing and node reuse etc work out so perfectly); must have been fun, thanks for sharing! I don't know / haven't thought much about text editors so a question for the authors or anyone who understands: from the mention of "the bracket pair AST", it seems that a separate AST is created just for this bracket-pair problem, is that right? I imagine there was/is already (at least one) another AST already being computed in the editor, for other reasons? If so, how did you decide between trying to do this with the same AST (making that one more complex), versus computing an additional AST just for this problem?