While you’re editing an article element, e.g. body text, no other user can edit the same element, but:

•Other users can edit other elements of the same article, if not opened by you. Thus, do not open article elements you do not intend to edit right on.

•Other users can edit the structure of article, if not checked-out by you.

•Other users can edit meta data of the article, if not in editing by you.

•A page designer can link the article to shape on page, even if you’re editing it, and assign/change format to the article.