$post['usergroupid'] and <if> Questions

[UberMensch]

I'm trying to do this in the postbit_legacy:

<if condition="$post['usergroupid'] == 8"> (If the post OWNER's usergroup id is 8)
  <!-- HTML here -->
<else />
  <!-- More Code -->
</if>

I'm pretty sure the "$post['usergroupid']" part is wrong. Is there a list of all the $post/$bbuserinfo variables?

Also, which conditions are allowed in the <if> statements? Are they similar/the same as php?