[Standards] ( XEP-0449) Are packless stickers legal?

Hi all and llarma (XEP-0449 author) in particular, It's not clear in the spec whether it is allowed to have a <sticker> element without "pack" attribute. I know that the XEP is mostly about specifying how packs work; but I am looking for a way to convey the information that an attachment is a sticker. My use-case is between slidge and movim (for now, but maybe other client devs are interested…), and not in a "pack" context. We could use a non-standard element, but if you intended to make packless XEP-0449 stickers legal, let's use your XEP! Basically, we would just add an empty <stickerxmlns='urn:xmpp:stickers:0' />to an attachment (specified via oob and/or SIMS and/or SFS -_-). Did you intend to make this legal or should we use something else? Thanks for your reply, -- nicoco