code: def get(self, tag, default=None):
          
          full_tag = 'Xmp.pyctools.' + tag
          if full_tag in self.data:
              return self.data[full_tag]
          return default
docs: Get a metadata value.
  
          Each metadata value is referenced by a ``tag`` -- a short
          string such as ``'xlen'`` or ``'audit'``. In the sidecar file
          these tag names are prepended with ``'Xmp.pyctools.'``, which
          corresponds to a custom namespace in the XML file.
  
          :param str tag: The tag name.
  
          :returns: The metadata value associated with ``tag``.
  
          :rtype: :py:class:`str`