Ranking of liturgical days in the Roman Rite

Ranking of liturgical days in the Roman Rite serves two purposes. The rank indicates some particular points about the manner of celebrating the day: for instance, the Mass of a Solemnity will include recitation of Gloria in Excelsis and Creed, that of what is now called in a specific technical sense a Feast will have Gloria but not Creed. and a Memorial will have neither. The other purpose is to determine which Mass is to be said when two feasts coincide (or "occur") on the one day, as well as when a feast falls on a Sunday or certain other privileged days.