docs: def _format_src_url(self, path, caller_system):
          """
          Ensure path is absolute and use the correct URL format for use with
          cross Azure storage account copy function.
  
          Args:
              path (str): Path or URL.
              caller_system (pycosio.storage.azure._AzureBaseSystem subclass):
                  System calling this method (Can be another Azure system).
  
          Returns:
              str: URL.
          """
          path = '%s/%s' % (self._endpoint, self.relpath(path))
  
          # If SAS token available, use it to give cross account copy access.
          if caller_system is not self:
              try:
                  path = '%s?%s' % (path, self._storage_parameters['sas_token'])
              except KeyError:
                  pass
  
          return path