def load(self, content):
        """Loads Command Definitions from the given YAML content into
        into this Command Dictionary.  Content may be either a
        filename containing YAML content or a YAML string.

        Load has no effect if this Command Dictionary was already
        instantiated with a filename or YAML content.
        """
        if self.filename is None:
            if os.path.isfile(content):
                self.filename = content
                stream        = open(self.filename, 'rb')
            else:
                stream        = content

            for cmd in yaml.load(stream):
                self.add(cmd)

            if type(stream) is file:
                stream.close()