<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _split_scheme(expression):
 """ Splits the scheme and actual expression :param str expression: The expression. :rtype: str """

        match = re.search(r'^([a-z]+):(.*)$', expression)
        if not match:
            scheme = 'plain'
            actual = expression
        else:
            scheme = match.group(1)
            actual = match.group(2)

        return scheme, actual