allow underscores in an emoji shortcode

30.md

@@ -14,7 +14,7 @@ Custom emoji may be added to **kind 0** and **kind 1** events by including one o
 
 Where:
 
-- `<shortcode>` is a name given for the emoji, which MUST be comprised of only alphanumeric characters.
+- `<shortcode>` is a name given for the emoji, which MUST be comprised of only alphanumeric characters and underscores.
 - `<image-url>` is a URL to the corresponding image file of the emoji.
 
 For each emoji tag, clients should parse emoji shortcodes (aka "emojify") like `:shortcode:` in the event to display custom emoji.
@@ -53,4 +53,4 @@ In kind 1 events, the `content` should be emojified.
   "pubkey": "79c2cae114ea28a981e7559b4fe7854a473521a8d22a66bbab9fa248eb820ff6",
   "created_at": 1682630000
 }
-```
+```