This question was posted in response to the following article: http://help.adobe.com/en_US/ColdFusion/10.0/CFMLRef/WSc3ff6d0ea77859461172e0811cbec22c24-7 5a8.html
Name attribute is actually optional for action="join". If omitted, then all threads are joined. The "Req/Opt" & "Description" for the name attribute should probably be updated.
CFB should also not flag the name attribute as required for action="join".