JSON::PP is a pure perl JSON decoder/encoder (as of RFC4627, which we know
is obsolete but we still stick to; see below for an option to support part
of RFC7159), and (almost) compatible to much faster JSON::XS written by
Marc Lehmann in C. JSON::PP works as a fallback module when you use JSON
module without having installed JSON::XS.

Because of this fallback feature of JSON.pm, JSON::PP tries not to be more
JavaScript-friendly than JSON::XS (i.e. not to escape extra characters such
as U+2028 and U+2029 nor support RFC7159/ECMA-404), in order for you not to
lose such JavaScript-friendliness silently when you use JSON.pm and install
JSON::XS for speed or by accident. If you need JavaScript-friendly
RFC7159-compliant pure perl module, try JSON::Tiny, which is derived from
Mojolicious web framework and is also smaller and faster than JSON::PP.

JSON::PP has been in the Perl core since Perl 5.14, mainly for CPAN
toolchain modules to parse META.json.