Dress of the clergy has changed since the modifications following the Second Vatican Council. This occurred not only in the Roman Communion, but in the Anglican Communion and other Catholic jurisdictions. Today, the most widely-identifiable marker of a Catholic cleric is the clerical collar. This is a relatively new invention and is widely believed to have originated when an Anglican priest turned his regular collar around backwards and started wearing it without a tie (collars were detachable from shirts back then). More recently, the "tab collar" made its way onto the clerical stage. Yet, the clerical collar is in fact not the primary emblem of a cleric. (Spoiler alert: The real symbol of the clerical state is the tonsure. Keep reading for more about that later.) In fact, clerical neck wear has changed over the years. Observe the following painting, entitled Portrait of a Cleric, by Allesandro Allori in the 16th century. The collar is certainly different and much more like a "regular" dress shirt collar of today.
Abito corto was worn much like the cassock from which it derived. The zucchetto (skull cap) was worn with it by all ranks. The zucchetto is white for the Pope, red for Cardinals and many Prince-Bishops, purple for Bishops, and black for priests and other clerics. Certain prelates who are not Bishops have black zucchetti with purple or red trimming. So, abito corto was merely modified clerical habit for street wear as opposed to street clothes redesigned to be "clerical." There is an important distinction between the two from a philosophical, theological, and canonical standpoint.
Observe the following 19th century cleric in abito corto, including the zucchetto:
So what was worn before the cassock became street dress and abito corto was developed? It was typical for secular clergy who were out and about town to dress like the gentlemen of their day, with appropriate modesty, complete with zucchetto. (Remember the tonsure, represented by the zucchetto, is the main symbol of the clerical state.) In other words, they were either in their habit (the cassock) or they were in regular gentleman's street dress, properly adorned to represent the clerical state. This is believed to have been typical from the Medieval period well into the 18th century and was still certainly seen thereafter.
This brief journey through the history of clerical dress leads back to the decision made by the Patriarchal See earlier this year. The modern clergy suit has been abolished, as have shirt and trouser combinations. The cassock is the primary clerical habit of all ranks of the clergy, as it has always been. Clerics are, by canon law, entitled to wear the cassock and cannot be told not to wear it in favor of another form of dress.
Traditional abito corto has been retained to provide an alternative to the cassock when appropriate. Both the Roman/Anglican version with the knee-britches and the Baltimore version with full-length trousers are included as options, and both are worn with the zucchetto.
Following ancient custom, a lay-style suit is also permitted as regular street-wear under certain circumstances, provided it is in accordance with the modesty of the clerical state. The zucchetto is the norm. Bishops wear the ring and pectoral cross. Other clerics may wear a simple silver pendant cross. Various other elements of this version of clerical dress are distinctly in the clerical counterpart to lay usage, such as gloves.
The Patriarchal See has a sacred duty to maintain the heritage and traditions of the Church. It was with this in mind that, after due reflection, prayer, study, and discussion that these modifications were made to the norms of clerical dress for this Particular Church. These modifications to a more traditional usage better place the clergy under the Patriarchal See within the historical context of the Church as traditional clerics with a mandate of mission, service, and charity.