note that this still doesn't fix the next error message for compilation which is
fatal error: Not a markup command: line which is triggered by the *definition* of the markup macro: (defmacro*-public markup (#:rest body) .. (car (compile-all-markup-expressions `(#:line ,body)))) the markup compilation tries to lookup the 'line' markup dynamically, and fails. https://codereview.appspot.com/575930043/
