Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Perl 6 is a programming language specification. It serves as a major revision to Perl, introducing elements of many modern and historical languages. Perl 6 is intended to have many implementations. Backward compatibility with earlier versions of Perl is not a direct goal, though a compatibility mode is part of the specification. The design process for Perl 6 began in 2000. Development on Pugs, the first implementation, began in 2005, and today there are multiple Perl 6 implementation projects. Rakudo Perl is based on Parrot and PGE, and releases a new version every month; as of February 2010[update], the project has released 26 stable versions. SMOP is written in C. Larry Wall maintains a reference grammar known as STD.pm, written in Perl 6 and bootstrapped with Perl 5.