Worth noting that black_hidden is allegedly drawn in Sven Co-op, according to this wiki's Tool textures page. I haven't personally verified this; it's probably either an issue with SCHLT or that Sven assumes lightmapped surfaces are drawn.
A couple things I want to note, but am not putting directly on the page (as it's an archived tutorial):
The TGAs used for detail textures can be RLE compressed, as long as they don't have an alpha channel (they don't use it anyway).
I think 512x512 detail textures are supported on modern hardware; don't quote me on that, though.
Users whose GPUs have blocked the GL_ARB_multitexture extension (such as for enabling overbright lighting without Xash) will not be able to enable detail texturing.
As of late 2019, detail textures on non-power-of-two WAD textures do not display correctly when mipmapping is enabled (unless gl_round_down is enabled, probably).
doors/doormove.wavanddoors/doorstop.wavifmovesndandstopsndare non-zero.black_hiddenis allegedly drawn in Sven Co-op, according to this wiki's Tool textures page. I haven't personally verified this; it's probably either an issue with SCHLT or that Sven assumes lightmapped surfaces are drawn.GL_ARB_multitextureextension (such as for enabling overbright lighting without Xash) will not be able to enable detail texturing.gl_round_downis enabled, probably).