“On [Archive of Our Own, a.k.a.] AO3, users can put in whatever tags they want. (Autocomplete is there to help, but they don’t have to use it.) Then behind the scenes, human volunteers look up any new tags that no one else has used before and match them with any applicable existing tags, a process known as tag wrangling.”
—Samantha Puc, “Fans Are Better Than Tech at Organizing Information Online.” Wired. June 11, 2019.
There’s been lots of discussion of the significance of AO3’s Hugo Award for Best Related Work.
Modest proposal? Use this process on new terms entered in the search box of a library’s online catalog to surface subject headings for users. It’s a logical extension of the catalogers work.