I have always noticed that sectors in UDMF have the ability to store custom fields. In GZDoombuilder, it looks like there is a whole lot of different data that you can store in that.
Spoiler:Now, if I define one of those fields, in what way can I access that data? Can I use them in ACS, can they only be retrieved with ZScript, do they have other purposes, or is that purely a GZDB organisation-type thing? I couldn't find anything on the wiki about it.