Parse a top-level template string Expression. Any extraneous text
    is considered literal text.

def _parse(template):
    """Parse a top-level template string Expression. Any extraneous text
    is considered literal text.
    """
    parser = Parser(template)
    parser.parse_expression()

    parts = parser.parts
    remainder = parser.string[parser.pos:]
    if remainder:
        parts.append(remainder)
    return Expression(parts)