”When I did JavaScript's regular expressions I was looking at Perl 4. I did step through it in the debugger, as well as read the code. And that gave me ideas; the implementation I did was similar. In this case the recursive backtracking nature of them was a little novel, so that I had to wrap my head around. It did help to just debug simple regular expressions, just to trace the execution. I know other programmers talk about this: you should step through code, you should understand what the dynamic state of the program looks like in various quick bird's-eye views or sanity checks, and I agree with that.” Brendan Eich in “Coders at Work: Reflections on the Craft of Programming” Peter Seibel 2009 page 158/159