code: function UpElement(tag) {
    var parts = tag.split(/([#.])/);
    tag = parts.shift();
    var elt = document.createElement(tag);
  
    while (parts.length) {
      let symbol = parts.shift();
      let val    = parts.shift();
      switch (symbol) {
      case '#': elt.id = val;           break;
      case '.': elt.classList.add(val); break;
      }
    }
    
    return elt;
  }
docs: ## UpElement
  
  Create an element.
  Support low-level sugar in form of `div#id.class`.