def METHOD_NAME(cls, source: Class, attr: Attr) -> bool:
    """
    Convert string literal default values to enumeration members
    placeholders and return result.
    The placeholders will be converted to proper references from the
    generator filters.
    Placeholder examples: Single -> @enum@qname::member_name
    Multiple -> @enum@qname::first_member@second_member
    """
    assert attr.default is not None
    value_members = {x.default: x.name for x in source.attrs}
    name = value_members.get(attr.default)
    if name:
        attr.default = f"@enum@{source.qname}::{name}"
        return True
    names = [
        value_members[token]
        for token in attr.default.split()
        if token in value_members
    ]
    if names:
        attr.default = f"@enum@{source.qname}::{'@'.join(names)}"
        return True
    return False