That’s a good case. If I’m making several notes and one of them happens to be a quotation, but I’m not interested in keeping track of quotations, then I might add “Quotation” to $Tags and move on. As time passes, though, I might realize this set of notes is becoming more focused on references and quotations. So I could decide to add a boolean key attribute $Quotation and maybe add the Reference prototype to my document, with its key attributes. So then I would browse my notes with Attribute Browser, find the ones tagged “Quotation” and adjust their attributes to be more formal by clicking $Quotation = true and file in some of the reference information if I have it or can locate it.
This is a case of “incremental formalization”, which Mark writes about frequently. I started the document with an informal, occasional use of tags, and evolved from there – gradually going back over my notes, curating them, and formalizing the portion of my document that contains notes with quotations.