Rinku does not, and this disparity can cause confusion at times. Underscores aren't "meant" to be in domain names but subdomains with them do resolve and so are valid by use. Rinku should support this.
Note that this does not extend to underscores in the registrable domain:
Opened from an internal issue (gh#106307) —
cmark-gfm's autolinker will happily autolink subdomains with underscores in them. Live example:https://abc_def.google.com
Rinku does not, and this disparity can cause confusion at times. Underscores aren't "meant" to be in domain names but subdomains with them do resolve and so are valid by use. Rinku should support this.
Note that this does not extend to underscores in the registrable domain:
https://abc_def.com
This is not valid, and Rinku and
cmark-gfmboth correctly disallow it. This should be maintained in the face of a fix.