The Perl PPI Parser has provided an essential building block for Perl 5 code analysis, documentation, and refactoring tools. Perl::Critic[25] uses PPI to critique Perl source code against the criteria in Perl Best Practices; the Padre IDE uses PPI for code analysis and refactoring. The PPI documentation makes reference to the truism that "Only perl (the interpreter) can parse Perl (source code)" because it is a dynamic language; a post on PerlMonks posits a formal proof.[26]