(2020-07-21, 23:02)Orion Pobursky Wrote: I don't see it that way. There always needs to be a fallback to produce a part without holes in non-TEXMAP compliant renderers (and TEXMAP is not required by the file format spec so we have to honor that). With NEXT you don't get fallback at all. With geometry2 you might but even the spec itself discourages it's use. Therefore it's better and simpler to just say no NEXT, no geometry2, and all fallback geometry goes in geometry3.
That is definitely not true. I believe that you are misunderstanding TEXMAP.
If the texture is drawn over a single quad, then the blank version of that exact same quad is perfectly legal. In this case, that quad would be a geometry2 quad, and would logically use !TEXMAP NEXT, since it's a single geometry line. If a texture is displayed over multiple triangles and/or quads, then START/END is required, but omitting the texture would still show blank geometry in the same place, as long as they use geometry2.
Obviously, anything in the geometry1 section would be ignored by non-TEXMAP compliant renderers. So, if there is a geometry1 section, then it is almost certain that there should also be a FALLBACK section. Requiring this in the official parts spec is reasonable. But the easiest way to make a textured part is to simply leave the textured geometry blank for non-TEXMAP compliant renderers. So disallowing NEXT and geometry2 in official parts is wrong.