See to <http://www.json.org/> and "RFC4627"(<http://www.ietf.org/rfc/rfc4627.txt>).
This module converts Perl data structures to JSON and vice versa using either
JSON::XS or JSON::PP.
JSON::XS is the fastest and most proper JSON module on CPAN which must be
compiled and installed in your environment.
JSON::PP is a pure-Perl module which is bundled in this distribution and
has a strong compatibility to JSON::XS.
This module try to use JSON::XS by default and fail to it, use JSON::PP instead.
So its features completely depend on JSON::XS or JSON::PP.