I'm an EE and was looking for some potential open source or similar projects to contribute to. Because the spec is available online and it's got some cool digital aspects, as well as a few systems in my region, I thought I'd take a look at TETRA (maybe osmocom-tetra or something). I do have one question though. Looking at the spec (EN ETSI 300 392-2 section 18.104.22.168) it says that there are multiple types of Broadcast PDU. If the "broadcast type" field is 00 then it's a SYSINFO PDU, which is one of the first things I wanted to decode. 01 is an ACCESS-DEFINE PDU. 10 is a SYSINFO-DA PDU, which is a SYSINFO message for QAM. But then 11 says "Reserved." What does that mean? What if data comes with that type, what to do with it? Is there any place that's used? Does it just mean they will introduce the spec later or that manufacturers can do what they want with it?