---
summary: Grammar for room aliases
---
created: 2016-04-19 11:36:13.0
creator: richvdh
description: |-
  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?
id: '12634'
key: SPEC-391
number: '391'
priority: '3'
project: '10001'
reporter: richvdh
status: '1'
type: '2'
updated: 2016-10-28 16:28:30.0
votes: '0'
watches: '2'
workflowId: '12734'
---
actions:
- author: richvdh
  body: |-
    From [~matthew]:

    {quote}
    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
    {quote}
  created: 2016-04-19 12:15:53.0
  id: '12856'
  issue: '12634'
  type: comment
  updateauthor: richvdh
  updated: 2016-04-19 12:15:53.0
- author: richvdh
  body: |-
    From [~eternaleye]: 
    {quote}
    The zero-width joiner, in particular, is [needed to construct the letterforms of some languages that Unicode does not support sufficiently|https://modelviewculture.com/pieces/i-can-text-you-a-pile-of-poo-but-i-cant-write-my-name].
    {quote}
  created: 2016-04-19 12:26:31.0
  id: '12860'
  issue: '12634'
  type: comment
  updateauthor: richvdh
  updated: 2016-04-19 12:26:31.0
- author: richvdh
  body: |-
    https://github.com/matrix-org/matrix-doc/blob/human-id-rules/drafts/human-id-rules.rst proposes:

    {quote}
    * 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/
    {quote}
  created: 2016-04-19 12:55:50.0
  id: '12863'
  issue: '12634'
  type: comment
  updateauthor: richvdh
  updated: 2016-04-19 12:55:50.0
- author: richvdh
  body: 'Migrated to github: https://github.com/matrix-org/matrix-doc/issues/668'
  created: 2016-10-28 16:28:30.0
  id: '13477'
  issue: '12634'
  type: comment
  updateauthor: richvdh
  updated: 2016-10-28 16:28:30.0