This change is causing no end of headaches. I have wasted a day already fixing things that are now broken on account of this.
Turns out built-in-formats.xsd is *not* only used by our internal tests. It is part of the TDML runner's tdml:defineSchema infrastructure - included into every such embedded schema implicitly. TDML runner is callable/usable from our CLI, which means it is part of the published non-test daffodil jars. built-in-formats.xsd and daffodilTest1 are also is "out there" in that they appear on slides that are full of small examples that have been published on the web for a while now. I think this horse has left the barn, and we're committed to supporting built-in-formats.xsd as is, in the original location as part of daffodil-lib. If we want to deprecate it in the future in favor of some better named thing I'm fine with that. But changing this is going to require a deprecate, and slow-cut over, otherwise it requires a big comprehensive sweep hundreds of lines of code change, subtle bugs come up. And the changes have to be done in lots of things that aren't even part of the apache daffodil code base. Also unless DAFFODIL-900 is fixed (missing diagnostic on dfdl:ref not found), changing any of this stuff is very dangerous.