The Constitutions of Clarendon, 1164 - however it only contains 16 points. (But it does say at the end "There are, indeed, many other great customs and dignities of holy mother church and of the lord king and barons of the kingdom, which are not included in this writing, but which are to be preserved to holy church and to the lord king and his heirs and the barons of the kingdom, and are to be kept inviolate for ever."

"Carol" just means song with a secular tune, as opposed to plain chant - the idea that Carols have to have something to do with Christmas is a modern idea. (Though in fact Thomas was martyred on the fifth day of Christmas, on December 29th, so in this case there is a seasonal connection.