If the string you are looking for is guaranteed to be at position 24 and be 11 characters long, then substr is appropriate.

Otherwise, using a regular expression might be a more general solution. If you provide a few more examples of your data, you will probably get more advice.

Despite your node title, your question seems to have nothing to do with XML parsing. If you can provide a very small sample of your actual XML file, again, you will probably get more advice.