The Explain facility is the primary mechanism for Z39.50 clients to discover servers' capabilities. Explain-based clients can dynamically configure their user interface (or other search capabilities) to exactly match individual servers. This allows generic clients to access a wide range of Z39.50 server, and allows any client to adjust to changes in server configuration.
The Explain facility is defined by an abstract record structure and attribute set, with no additional protocol mechanisms. Still, effectively using Explain is a relatively large undertaking. This paper describes the most important issues to be considered, and suggests the most important features to implement first.