The editors of an overlay journal locate suitable material from open access repositories and public domain sources, read it, and evaluate its worth.
Or the editor may simply link to the article, via the table of contents of the overlay journal.
Episciences is an initiative by the Center for Direct Scientific Communication to host overlay journals.
In 2019, JMIR Publications, an open access publisher, announced the creation of a series of "superjournals", named JMIRx (JMIRx.org), which are overlay journals for preprint servers such as medRxiv, bioRxiv and PsyArXiv.
[4] That same year, the journal Physical Review began to link to pre-prints that they had accepted, but not yet published.