text: According to the spec, character references may cause surrogate
  characters (0xD800 to 0xDFFF) to be inserted into the DOM. Assuming
  that the DOM is an UTF-16BE environment, &#xD800;&#xDC00; and
  &#x10000; will both result in \xD800\xDC00 or U+1,0000. This should
  probably be pointed out explicitly since extra processing has to be
  done to achieve the same result in a parser that is not built atop
  UTF-16BE.
  Furthermore, it is not entirely clear whether a mixed form like
  \xD800&#xDC00; encoded in UTF-16BE should give \xD800\xDC00 or \xFFFD
  \xDC00. Not all browsers convert unpaired surrogates in UTF-16 to U
  +FFFD, so the mixed form may be interpreted as U+1,0000.
  --
  Øistein E. Andersen