Okay, so quality of service enforcement under MPLS isn't quite cutting-edge technology. However, until recently, MPLS QoS markings have always made use of a field in the MPLS label header designated "Experimental" (Exp) as defined in RFC 3032.
Recently released RFC 5462, a proposed standard, renames the Experimental field to the Traffic Class (TC) field. This is a change in name only; everything you know and love about 3-bit QoS markings remains the same. So why the update? From RFC 5462:
The EXP field, from the start, was intended to carry "Class of Service" (CoS) information. The field was actually called the "Class of Service field" in early versions of the working group document that was published as RFC 3032. However, at the time that RFC 3032 was published, the exact usage of this "Class of Service" field was not agreed upon and the field was designated as "experimental use"; hence, the name has since been the "EXP field".
The designation "for experimental use" has led other Standards Development Organizations (SDOs) and implementors to assume that it is possible to use the field for other purposes. This document changes the name of the field to clearly indicate its use as a traffic classification field.
(Why do I know this? I subscribe to the IETF's New RFCs RSS feed.)