I think most journals want to publish work that hasn't already been published somewhere. Particularly if they're paying writers for their work (not that all pay; we do). There are a lot of writers out there with great new work to share, and we want to give space to that new work. Journals may have different ideas about what "published" means. Videos of someone reading at an open mic, social media posts, blogs, a journal published in another country, work already published in a collection . . . there are many interpretations of "previously published." I read an article by one editor who wants to use the term "curated" instead of published. The publishing landscape is always evolving. I think the important thing is to be honest with the journal publishing your work and to ask any questions you might have. Honesty and communication--super important. If you're presented with a contract that gives you pause, ask questions. For us, once the work is published on our site, the writer is free to include it in a collection or anywhere else. We're super happy when someone's work ends up on Best of the Net or some other award site/print publication. And it's good form for a writer to credit the journal that first published the work. That's my take on it. Hopefully others editors will weigh in. Always good to hear others' thoughts.