And how would that work? Let's assume I wrote BrainFuckStandardMD, the implementation for Brainfuck. I would base it solely on the spec published as Common Markdown. I would not in any way use the copyrighted code as basis for my implementation, so it is not derived from it. I don't use the name markdown, so that even the ficticious claim to a trademark would be void. On what grounds would he sue me?