Poetry written in couplets is sometimes varied by the introduction of a triplet, in which the third line is an alexandrine. This occurs in the following example from Dryden, which introduces a triplet after two couplets:

A But satire needs not those, and wit will shine
A Through the harsh cadence of a rugged line:
B A noble error, and but seldom made,
B When poets are by too much force betrayed.
C Thy generous fruits, though gathered ere their prime,
C Still showed a quickness; and maturing time
C But mellows what we write to the dull sweets of rhyme.