At least on a surface level, these are very similar: a description of the syntax to use when parsing some arbitrary CSS tokens. The only difference I can spot between the two definitions (1, 2) is that syntax can take a single *.

However, syntax takes this grammar wrapped in a <string>, and type() takes it unquoted, using a new <syntax> type. Is there a reason why type() can't also take a string, or has it just been overlooked?