One of the main problems to solve when implementing systems for distribution of music in the Web is the issue of digital rights. Even when the business model problem is clarified, there are still technical problems to solve, such as the interchange of digital rights information and the control over their use. Using a Rights Expression Language (REL) helps in solving this problem. Although there are several international initiatives to standardise a REL, we focus on the approach followed by MPEG-21, that in fact is trying to converge from existing alternatives. We present in this paper a new reference implementation of the ongoing REL standard, and we raise the idea of specifying a subset of it, i.e. a profile, to ease its implementation. By analysing what the existing Web sites for music distribution are doing, we come to the conclusion that a specific profile for music could be the starting point.