LPeg is a new pattern-matching library for Lua, based on Parsing Expression Grammars (PEGs). PEGs look similar to regular expressions or context-free grammars in Backus-Naur form (BNF) notation. PEGs make a good replacement for regular expressions, because they are strictly more powerful. For example, a regular expression inherently cannot find matched pairs of parentheses, because it is not recursive, but a PEG can.
