A minor clarification for those who might be learning from HN: regular expressions aren't equivalent to context-free grammars, they are even more limited than c

A minor clarification for those who might be learning from HN: regular expressions aren't equivalent to context-free grammars, they are even more limited than context-free grammars. Things which involve arbitrary-depth nesting or recursion, like HTML, can't be parsed by regular expressions, but that is exactly what context-free grammars are for. Where regular expressions correspond to finite state automata (essentially directed graphs where nodes are states and edges are input-driven transitions between states), context-free grammars correspond to pushdown automata (with a stack, this is the recursion secret sauce). Lots of interesting things are context-free. For example, any good programming language grammar should be context-free, to allow sane and efficient parsing. I welcome further corrections.