Walltexture is TEXTURES syntax, actually. Specifically, it's the syntax for a texture entry that cannot be used as a flat. SRB2 does not yet support using textures as flats, so we enforce the use of this syntax to ensure existing TEXTURES lumps continue to behave correctly when that feature is eventually added.Should be "wallTexture" instead of "Texture" for it to work in SRB2. Yeah, we fiddled the syntax a bit for some reason.