Summary:    This memo defines the Session Description Protocol (SDP).  SDP is  intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation.  This document obsoletes RFC 4566.
I think the document make sense and is written very clear, except some small nits:
# In Section 5, there are several terms that miss references, such as "US-ASCII subset of UTF-8",  "ASN.1 or XDR", etc.
# s/session- specific/session-specific/
# Suggest to add tags on "overview optional items" to identified now-obsolete items, such as "a=cat", "a=keywds", "k=".