Once the backlog of existing PMC articles is dealt with (cf. https://github.com/erlehmann/open-access-media-importer/issues?milestone=2 ), the bot should concentrate on articles newly indexed by PMC. This could be for one of three main reasons:
(1) an article is newly published in a journal indexed by PMC
(2) an article is submitted to PMC by a journal not indexed by PMC
(3) a journal becomes newly indexed by PMC, which may mean the addition of backfiles.

The bot should work for all three cases, with the order of priority being 1-3-2.