(PHP 5)
DOMCharacterData::substringData — Extracts a range of data from the node
$offset
   , int $count
   )Returns the specified substring.
offset
     Start offset of substring to extract.
count
     The number of characters to extract.
   The specified substring. If the sum of offset 
   and count exceeds the length, then all 16-bit units 
   to the end of the data are returned.
  
DOM_INDEX_SIZE_ERR
     
       Raised if offset is negative or greater than the
       number of 16-bit units in data, or if count is 
       negative.