References.md

Types of XMPP "References"

• Thread (in-reply-to); largely off-scope for our discussion
• References of things mentioned in the payload/body of a message (0372)
  • nicknames, URLs, old messages by means of xmpp: URI, etc.
  • multiple Reference elements are allowed
  • Can be used inside Attach-To to add References to a previous message
  • Can be sent by anyone
  • is irrelevant to MAM 2.0
• Attach-To for content that only makes sense in the context of another message
  • Usable for Reactions, Edits (former LMC), Retraction, Image / website previews, Receipts(?), Read Markers(?)
  • A message can be attached at-most to one other message (nobody could think of a case where it would be needed, Ge0rG still objects)
  • allows grouping / special handling by MAM 2.0, e.g. for thin clients
  • generally, the attached payload SHOULD be inside of the element (e.g. reactions)
  • for E2EE and legacy Last Message Correction, an without a payload implies that the sibling elements need to be reviewed
  • Some kinds of Attach-To can only be sent by the original author or a privileged entity (bot/admin in MUCs)
  • Attach-To messages SHOULD NOT be nested, i.e. attach-to another Attach-To message