ArbitraryMetadata is an idea taken from [[http://monotone.ca|Monotone]]

It allows to attach signed key-value pairs to a revision/file after a commit and a key may be used more than once.

In monotone this is not only used for the usual commit metadata like time, author, commit-messages,
but also for tracking extra information like core developer approvals or testresults.

The common use-case is "trust" based update to 
   * revisions with approval of n core devs
   * revisions that passed the testsuite on a set of buildbots



== The way Monotone handles it ==

The metadata is stored using 2 Ideas.



Examples:
{{{#!rst

Statement
  links a key-value pair to a revision

  :revision: 73268e317ad3
  :name: push-date
  :value: 2003-03-03 22:00:31 UTC

Certificate
  signs a Statement


  :revision: 73268e317ad3
  :name: push-date
  :value: 2003-03-03 22:00:31 UTC
  :signed-by: john@doe.com
  :signature: 1234

}}}

== Basic Properties of the Metadata ==

 * immutable - we don't want to change the things we added
 * unversioned - we can't change it, so we wont need to version it
 * keys are not unique - more than one person might add the same thing, it just has to work



== How could mercurial do it ==

XXX: todo

See also PushkeyConcept.