So all elements will be grouped together under this single marked up
item. This works by first determining the parent element of the first item
in the list. It then moves all of the matching elements under the wrapper
and inserts the wrapper where that first element was found. (This is in
accordance with the way jQuery works.)
Markup is usually XML in a string, but it can also be a DOMNode, a document
fragment, a SimpleXMLElement, or another DOMNode object (in which case
the first item in the list will be used.)