def help_description(s="", compact=False):
    """
    Append and return a brief description of the Sage documentation builder.

    If 'compact' is ``False``, the function adds a final newline character.
    """
    s += "Build or return information about Sage documentation. "
    s += "A DOCUMENT and either a FORMAT or a COMMAND are required."
    if not compact:
        s += "\n"
    return s