(PHP 5, PHP 7)
DOMCharacterData::substringData — Extracts a range of data from the node
$offset
   , int $count
   )Returns the specified substring.
offsetStart offset of substring to extract.
countThe 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.