The CPAN Meta Spec has gone through several iterations.
It was originally written in HTML and later revised into POD (though published in HTML generated from the POD).
Fields were added,
removed or changed,
sometimes by design and sometimes to reflect real-world usage after the fact.
This document reconstructs the history of the CPAN Meta Spec based on change logs,
repository commit messages and the published HTML files.
In some cases,
particularly prior to version 1.2,
the exact version when certain fields were introduced or changed is inconsistent between sources.
When in doubt,
the published HTML files for versions 1.0 to 1.4 as they existed when version 2 was developed are used as the definitive source.
Starting with version 2,
the specification document is part of the CPAN-Meta distribution and will be published on CPAN as CPAN::Meta::Spec.
specification version numbers will be integers and decimal portions will correspond to a release date for the CPAN::Meta library.
Revised spec examples as perl data structures rather than YAML
Switched to JSON serialization from YAML
Specified allowed version number formats
'recommends' and 'conflicts' with new 'prereqs' data structure divided by phase (configure,
etc.) and relationship (requires,
Added support for 'develop' phase for requirements for maintaining a list of authoring tools
Changed 'license' to a list and revised the set of valid licenses
Made 'dynamic_config' mandatory to reduce confusion
Changed 'resources' subkey 'repository' to a hash that clarifies repository type,
url for browsing and url for checkout
Changed 'resources' subkey 'bugtracker' to a hash for either web or mailto resource
Changed specification of 'optional_features':
Added formal specification and usage guide instead of just example
Changed to use new prereqs data structure instead of individual keys
Clarified intended use of 'author' as generalized contact list
Added 'release_status' field to indicate stable,
testing or unstable status to provide hints to indexers
Added 'description' field for a longer description of the distribution
Formalized use of "x_" or "X_" for all custom keys not listed in the official spec
Added required 'meta-spec' field to define 'version' (and 'url') of the CPAN Meta Spec used for metadata
Added 'provides' field
Added 'no_index' field and deprecated 'private' field.
'no_index' subkeys include 'file',
'package' and 'namespace'
Added 'keywords' field
Added 'resources' field with subkeys 'homepage',
Added 'optional_features' field as an alterate under 'recommends'.
'requires_os' and 'excluded_os' as valid subkeys