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Yep, just line.length - 4.

Think about what portion of the given line you want to highlight: You want to highlight everything after the 4th character in a given line. The length of this is not just line.length(), but...

I started debugging by "removing" code until things start to "work" (a.k.a. don't throw exceptions/do anything unexpected, not necessarily do what the final code should do).

First, I commented out...