Mechanism limiting Normal Weapons from holding non-ammunition?
 

I'm working on data files that allow characters to customize various bits of gear via inventions. The way I've figured best how to do that (without being able to see beyond the veil of LWD's Pathfinder files) is to dynamically assign "thing.holder" to viable equipment, and then place the invention pick into the target gear. For the most part, this works, but when I try to use it on a weapon present on the wTable portal (under the Other Weapons title bar), only ammunition picks can be placed in the holder.

I know that the <holdlimit> element accomplishes this, but there aren't any included in the <thing> elements for the weapons placed here. Is there a <holdlimit> on one of the components, or is there another mechanism at work here: if so, are there ways for me to dynamically affect that mechanism?

(PS I'm aware that I can get around this asking users to add a iMagWeapon pick to customize normal weapons. But in the interest of keeping it as user-friendly as possible I'd also benefit from targeting picks with thing.holder & telling those picks to adhere to a certain tag expression :D ).