if path1 is subpart of path2, get the next path item.
    example:
    path1 = '/foo'
    path2 = '/foo/bar/foo'
    -> 'bar'

def content_item(path1, path2, path_sep='/'):
    """
    if path1 is subpart of path2, get the next path item.
    example:
    path1 = '/foo'
    path2 = '/foo/bar/foo'
    -> 'bar'

    """
    p1_parts = path1.split(path_sep)
    p2_parts = path2.split(path_sep)
    # special case when path1 is root
    if path1 == path_sep and len(p2_parts) >= 2:
        return p2_parts[1]
    if len(p2_parts) <= len(p1_parts):
        return ''
    for i, item in enumerate(p1_parts):
        if item != p2_parts[i]:
            return ''
    return p2_parts[i+1]