Return a list of rendered weighted spans for targets.
    Function must accept a list in order to select consistent weight
    ranges across all targets.

def render_targets_weighted_spans(
        targets,  # type: List[TargetExplanation]
        preserve_density,  # type: Optional[bool]
    ):
    # type: (...) -> List[Optional[str]]
    """ Return a list of rendered weighted spans for targets.
    Function must accept a list in order to select consistent weight
    ranges across all targets.
    """
    prepared_weighted_spans = prepare_weighted_spans(
        targets, preserve_density)

    def _fmt_pws(pws):
        # type: (PreparedWeightedSpans) -> str
        name = ('<b>{}:</b> '.format(pws.doc_weighted_spans.vec_name)
                if pws.doc_weighted_spans.vec_name else '')
        return '{}{}'.format(name, render_weighted_spans(pws))

    def _fmt_pws_list(pws_lst):
        # type: (List[PreparedWeightedSpans]) -> str
        return '<br/>'.join(_fmt_pws(pws) for pws in pws_lst)

    return [_fmt_pws_list(pws_lst) if pws_lst else None
            for pws_lst in prepared_weighted_spans]