The one Matt Pietrek is associated with, but which is no longer available at the original address. - Please note that this is one of the official CodeView 4, it does not apply to the CodeView 5 format.
Update: I found a copy of the CV4 Symbolic Debug Information Specification document. This is revision 4 of December 1, 1995. Compared to the document linked above, it contains an additional chapter “8. TypeServer API” and an application with revision history, the rest is basically the same. All references to "Microsoft CodeView" have been replaced by "Mirosoft Symbol and Type." The original specification is marked as Microsoft Confidential, so I won’t release it, but it has no advantage over the document linked above.