唱词的英文：
libretto

The first line serves to introduce the mood, while the second line enunciates the theme.
唱词上句起兴，下句点明主题。

A chorus line
(歌舞喜剧中的)歌舞队唱词.

And needless to say, I would love to be of assistance in translating opera librettos
不用说，我也愿意协助翻译京剧唱词。

The tunes, too, match the two-part, four-line format.
曲调则全部是上下句体、4句唱词分两遍唱完。

They have four lines arranged in a folk meter, whereby the lines are not standard seven-word ones.
"花儿"的唱词为4句民间格律体，即它们不是规整的七言句式