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