code: function $(id) {
    var el = document.getElementById(id);
    return el ? assertInstanceof(el, HTMLElement) : null;
  }
docs: <include src="assert.js"> 
  Alias for document.getElementById. Found elements must be HTMLElements.
  @param {string} id The ID of the element to find.
  @return {HTMLElement} The found element or null if not found.