Tags
A label marks a document with one choice. Tags are as many words or phrases as you like: "flashback", "needs research", "London". Every document can have them, notes and research as well as scenes.
Adding tags
The inspector's Metadata section, the Scene drawer and the Outliner have a Tags row. Type a tag and press Return; type several with commas between them. The + beside the tags offers every tag the project already uses, with how many documents have it, so a tag is spelled the same way everywhere. To take a tag off, choose its ×.
Tags are tidied as you add them: spaces trimmed, and a tag already on the document, however it's capitalised, isn't added twice.
Finding everything with a tag
Choose a tag anywhere it appears and the contents are filtered by it: every document that has it, in its place in the book (see Filtering the Contents). The tile above the contents lists the project's tags under Tags, and the filter button offers them under Tag. The pencil on the filter's card keeps the filter as a collection; its × shows everything again.
A collection's rule can also be "Tag is flashback": a document matches when that is one of its tags. "Tag is" nothing matches documents with no tags.
Elsewhere
A Scrivener project's keywords come across as tags when it's imported, each document keeping the keywords it had. Re-importing merges them: a keyword added or removed in Scrivener since the last import is added or removed here, and tags added here stay.
In a journal, the Tags field is the same one its posts always had; {tags} in a post's opening or sign-off prints them. An AI assistant can read a document's tags and, if you let it set fields, replace them.
On a device running an older Five Rooms, tags show as a text field reading "flashback, London"; editing it there works, and the tags come back as tags here.