There is a single (AS) user on matrix.org who has a colon in their localpart,
but I suspect that is an artifact of old bridge code and won't work over
federation anyway.
Colons in MXIDs are particularly harmful because they make it impossible to
split mxids into local- and remote-parts
“Disclosure to Servers Within Chatroom” was indented lesser
than the surrounding threats.
Signed-off-by: Florian Jacob <projects+git AT florianjacob )DOT( de>
Adds the /msisdn' 3pid type and generally fleshes out what a 3pid
is and how they work.
This merges most of the work from Max Dor in https://github.com/matrix-org/matrix-doc/pull/1039
with some tweaks and additions.
