Every article has a set of contributors. These are individuals who have in one way or another directly helped with either the publication or the maintenance of a particular article. Contributors receive credit for being a part of the article's community, and have the ability to vote on future revisions to the article.
When an article is first published, all the article's authors, sponsors, and reviewers are immediately made article "contributors".
Any user who, in future, proposes a revision to an article that is subsequently accepted, automatically joins the community of article contributors.
If a user's judgment of proposed revisions to an article disagrees too frequently with the article Curator's, the user may lose status as an article contributor. It can be regained by contributing (and getting approved) a future revision to the article.