Predicate that returns True for custom attributes added to AttrTrees
    that are not methods, properties or internal attributes.

    These custom attributes start with a capitalized character when
    applicable (not applicable to underscore or certain unicode characters)

def tree_attribute(identifier):
    """
    Predicate that returns True for custom attributes added to AttrTrees
    that are not methods, properties or internal attributes.

    These custom attributes start with a capitalized character when
    applicable (not applicable to underscore or certain unicode characters)
    """
    if identifier[0].upper().isupper() is False and identifier[0] != '_':
        return True
    else:
        return identifier[0].isupper()