The Anglican Breviary has a unique possibility to simplify an Office by either Rule 1 or 2. This rule allows for the Office of the feria to be more strongly present than would otherwise be the case – especially if the Universal Kalendar is followed. In the Season of Lent the simplification of the Office is by Rule 2:
The foregoing Rule 1 is not applicable to any Office of semidouble or double rite which has proper III Nocturn Lessons, nor to an Office wherein a Commemoration must be made of another Office which has its own Homily (e.g., such as a common Vigil or a Lenten Feria, etc..). To cover such contingencies Rule 2 must be followed.
The Anglican Breviary, xli
As you will have noticed during Lent the ferias have a Gospel reading and a Homily proper to them. The above description tells us that because the Lenten Feria has a Homily (and Gospel) proper to it, it cannot be simplified by means of Rule 1. To simplify the Office of a Feast occuring on such a day Rule 2 must be used.
To reduce an Office of nine Lessons to three Lessons by Rule 2, Scripture must furnish Lesson i, whereupon the Legend can become Lesson ii, and the Homily Lesson iii, thus: for Lesson i is read Lesson i combined with Lesson ii from the occurrent Scripture, followed by Respond ii, except in Lent or on any other day without occurrent Scripture, in which case is read Lesson i (without adding Lesson ii) from the appropriate Common, with its Respond; then for Lesson ii is read the Legend, followed by its appropriate Respond (i.e., Respond iii from the Proper of the Season or the appropriate Respond from the Common, as the case may be); and for Lesson ii is read the Homily in whole or in part, followed by Te Deum.
The Anglican Breviary, xlii
So … what exactly is the rubric telling us to do? Reducing a nine Lesson Office to an Office of three Lessons is nothing more or less than simplifying (literally) an Office of double rank to that of a simple rank. Outside of Lent Rule 2 would put the occurrent Scripture of the nine Lesson Office in Lesson i, the Legend in Lesson ii, and the Homily in Lesson iii. Easy enough. A more complicated process must be followed for Rule 2 during Lent because a nine Lesson Office in lent will not have occurrent Scripture (it has a Gospel & Homily in the place of occurrent Scripture). In this case Rule 2 tells us that we need to turn to the Common which belongs to the nine Lesson Office in question and use Lesson i and Respond i from that Common as Lesson i of the Office to be said without adding Lessons ii and iii. Lesson ii will be the Legend (entire) followed by its appropriate Respond. For the iii Lesson the Homily (of the Lenten Feria) can be taken entire or in part without a Respond but in its place having the Te Deum.
Now there is an unclear phrase in the rubrics which I italicized above: followed by its appropriate respond. What does that mean? The Anglican Breviary is not very clear about what that means practically. I will therefore simply provide my own practice: I simply use the iii Respond from the Common in use. It seems to me that this meets the criterion of appropriateness which AB does provide.
I hope this will have clarified the Matins by Rule 2 we will be seeing during this season when the simplification of an Office is suggested. Questions are welcome, and if I can answer them I will. If someone else has a better or more appropriate answer that too is a welcome addition!