Hi Rachelle,
For a while we were marking up bills that had no short title with the "Popular Name" attribute using such a format, thinking that was the best way to identify references in bills with no other unique identifiers (Popular Name, Public Law number, US Code reference, Statutes at Large volume and page number). We are currently in the process of adding a NEW @entity-type value of "bill-by-number", which formats such citations at value="bill-by-number/[congress number]/[bill type]/[bill number]/[section]/[subsection]/etc." So the @value attribute on a "bill-by-number" citation for "HR 3099 of the 110th congress" would be value="billy-by-number/110/hr/3099", or "section 291(a) of HR 4508 of the 113th Congress" would be value="bill-by-number/113/hr/4508/s:291/ss:a". We have a few recent bills that include the citation, but it should be fully implemented in new bills this week.
But for most bills that have been marked up to this point, most can be identified with a @entity-type value of "act" and a @value value starting with "113". There should not be any distinguished with an "official title" property.
Let me know if this makes sense!
Molly B.