Exposition (qi) was called for in the first two lines; the development of the theme (cheng), in parallel verse structure, in the middle, or second and third, couplets; and the conclusion (he) in the final couplet.
Hundreds of Shangyin poems may be called "Wuti" (无题 – Untitled). It makes for an interesting challenge to select one to read. With that in mind, here is one such "Untitled" poem: number 215 from "300 Tang Poems" as posted online by the Chinese Text Initiative of the University of Virginia
Here is my translation:
The time since she left is hard to bear, as flowers wither after they lose their petals to the east wind.
Only in death do spring worms stop weaving silk; like candles provide light as they cry themselves into ash.
Clouds in the early morning mirror reflect her hair changing colour, the chant of the month feels cold in moonlight.
Magic mountain is near when you see no more road, pay attention green bird and carry her message to me.
For reference, here is the Google Translate output
When you meet difficult Bie Yinan, the Dongfeng weakness flowers residues.
Till death do us part, wax torch ashes tears dry.
Xiao-Jing but worry shallow change, night Yin should feel the moonlight cold.
Penglai this multi-channel, Bluebird attentive to peek.
And here is the translation by Witter Bynner.
Time was long before I met her, but is longer since we parted, and the east wind has arisen and a hundred flowers are gone.
And the silk-worms of spring will weave until they die, and every night the candles will weep their wicks away.
Mornings in her mirror she sees her hair-cloud changing, yet she dares the chill of moonlight with her evening song.
…It is not so very far to her Enchanted Mountain, O blue-birds, be listening!-Bring me what she says!