Return true if `x` is an HTML element. True when `x` is a vector
and the first element is a keyword, e.g. `[:div]` or `[:div [:span "x"]`.
Source
(defnelement?"Return true if `x` is an HTML element. True when `x` is a vector
and the first element is a keyword, e.g. `[:div]` or `[:div [:span \"x\"]`."[x](and(vector?x)(keyword?(firstx))))