Unless Perl 5 where the interpreter IS the de-facto specification, Perl 6 has the advantage of clear definition, which becomes clearer every day, since the language design team working on the syntax and the implementers finding ambiguous spots. Mainly the spec has 3 parts:

• The Synopses, the (almost) human readable documents which constantly kept up to date. (unlike other historic docs like apocalypses and exegese)
• http://feather.perl6.nl/syn, Other copies of the synopses:
• http://perlcabal.org/syn/ (alias URI to above)
• http://svn.perl.org/perl6/doc/trunk/design/syn/ (the source)
• http://perl6.cz/wiki/Synopses/en (Synopses on MediaWiki, with 'history' and 'watch' functions.)
• The Test Suite, which implementations has to pass, to deserve to be called "Perl 6".
• The STD.pm, a Perl 6 grammar, that defines the Syntax and is part of some implementations.

See Also:

• http://perl6.org/specification/