Tashriʿ constructs poetic lines that can end at more than one permissible point, often yielding two rhyme patterns. A longer version and a shortened version remain metrical and meaningful; it is also called tawshih dhā al-qāfiyatayn.
The poet arranges added material so that both the full and shortened forms work. Removing an ending arbitrarily, if it breaks sense or metre, does not constitute this device.