https://github.com/w3c/csswg-drafts/issues/2701#issuecomment-395504004 https://github.com/w3c/csswg-drafts/issues/2701#issuecomment... > Yeah, very intentional

https://github.com/w3c/csswg-drafts/issues/2701#issuecomment-395504004 https://github.com/w3c/csswg-drafts/issues/2701#issuecomment... > Yeah, very intentionally not allowed. It causes parsing issues, for one (you can't arbitrarily split up an ident and be guaranteed that both halves are still idents), and it's grammatically ambiguous with tagname selectors. There's an open issue https://github.com/w3c/csswg-drafts/issues/3748 https://github.com/w3c/csswg-drafts/issues/3748 "add note explaining that BEM `&__element` class accumulation isn't supported and why"