Check to see if a DOM node is within an XML document (or is an XML document).
Selects all direct child elements specified by “child” of elements specified by “parent”.
Determine if the callbacks have already been called at least once.
Determine if the callbacks list has been locked.
Selects all elements of type checkbox.
Determine whether an element has any jQuery data associated with it.
Escapes any character that has a special meaning in a CSS selector.