Well, I would certainly not call it illegal, but given what you have witnessed, it seems like it would be a good idea to use standard extensions for the contained files. The MPD spec makes absolutely no mention of filename extensions.
I'm at a loss as to why MLCad behaves that way. Having written LDView, I think I'd have to add extra code in order to get it to not recognize contained files that weren't .ldr/.dat.
I'm at a loss as to why MLCad behaves that way. Having written LDView, I think I'd have to add extra code in order to get it to not recognize contained files that weren't .ldr/.dat.