This site contains documents related to the development, use, and maintenance of the 2002 version of the Z39.86 standard. The National Information Standards Organization (NISO) provides the standard:
As a PDF file and in print for purchase.
2002 Version - DTDs and Other Resources
Errata, Proposed Changes, and Maintenance Activities for Z39.86-2002
"ZedVal" conformance validator for Z39.86-2002 DTBs
Background Information On Development of the Standard