Grammar for room aliases (SPEC-391)

[matrixbot]

Room aliases are intended to be

• human-readable
• unique

They have some structure: #<alias>:<homeserver>.

We need to specify a grammar for them, including which characters they may contain, and how they should be interpreted. Can they contain punctuation or whitespace characters? Should they be allowed to contain non-ascii characters, and if so, how should they be normalised? Should they be case-insensitive, and if so, in what locale?

(Imported from https://matrix.org/jira/browse/SPEC-391)

(Reported by @richvdh)

[matrixbot]

Jira watchers: @richvdh

[matrixbot]

Links exported from Jira:

relates to SPEC-1

[matrixbot]

From [~matthew]:

My thoughts for room alises and user ids: "utf8, with a blacklist of explicitly disallowed characters (all whitespace, *, /, :, ., any others we want to reserve). you're not allowed to mix charsets (fsvo charset), and possibly deny other homomorph attacks eg l v I".
IDs are compared case insensitively.

oh, and no zero length ids

-- @richvdh

[matrixbot]

From [~eternaleye]:

The zero-width joiner, in particular, is needed to construct the letterforms of some languages that Unicode does not support sufficiently.

-- @richvdh

[matrixbot]

https://github.com/matrix-org/matrix-doc/blob/human-id-rules/drafts/human-id-rules.rst proposes:

• MUST NOT contain a :
• MUST NOT contain one of the 107 blacklisted characters on this list: http://kb.mozillazine.org/Network.IDN.blacklist_chars
• After stripping " 0-9, +, -, [, ], _, and the space character it MUST NOT contain characters from >1 language, defined by the exemplar characters on http://cldr.unicode.org/

-- @richvdh

[aaronraimist]

It seems like this really needs to be addressed soon. I think room aliases should be lowercase only like user IDs otherwise it just creates confusion as to what room you are joining and "forces" you to add multiple similar aliases with different capitalization.

[Half-Shot]

The proposal is matrix-org/matrix-spec-proposals#1607 ?

[aaronraimist]

Thanks! It would have been nice if someone would have linked to it from here when it was proposed