Today, Friday and Saturday are the Advent Ember days or Quarter Tense days.
Today is also the feast of St. Eusebius which takes precedence over the ferial Office. At Mattins in the first nocturn as there is no occurring Scripture the lessons are taken from the Common, A Mileto, with their responsories. In the third nocturn the ninth lesson is the homily of the Ember Wednesday (all three lessons may be read as one, but the first of the three suffices for those with under an obligation for the Office). At Lauds the Ember Day is commemorated.
At Prime the Dominical preces are said as the feast of St. Eusebius is a semi-double.
Mass is sung after Terce and has the Gloria, second collect of the Ember Day (the first one given after the Kyrie in the Missal), the third collect of the BVM Deus, qui de beate and the last Gospel is of the Ember Day. Private Masses may be of the Ember Wednesday with its proper collect after the Kyrie Praesta, quaesumus and extra OT lesson. After Dominus vobiscum the collect Festina quaesumus is followed by a commemoration of St. Eusebius and then the collect Deus, qui de beate. As there is no Gloria the dismissal is Benedicamus Domino. The ministers of course wear violet folded chasubles.
In Collegiate and Cathedral churches two Masses are celebrated. The first is the Mass of St. Eusebius following Terce with the second collect Deus, qui de beate and third collect Ecclesiae etc., and the last Gospel In principio. After None the Mass of Ember Wednesday follows with second collect Deus, qui de beate and third Ecclesiae etc. with Benedicamus Domino as the dismissal. The ministers wear violet folded chasubles.
At Vespers there is a commemoration of Advent (using the collect of the preceding Sunday as the liturgy of feria ends with None). At Compline the Domincal preces are sung.
Traditionally, in England, today marked the start of the Great 'O' Antiphons with O Sapientia beginning a day earlier than the Roman Kalendar. As Rubricarius is in Limerick today that presents an interesting dilemma...
[Update: I rather doubt (with 99.99% certainty) that O Sapientia will be sung either today or tomorrow here in Limerick!]