XML Server Pages, or Extensible Server Pages.
An abstraction layer that allows code to be generated from markup.
XSPFundamentals: Basic architecture of XSP pages.
XSPSyntax : A quick reference to the XSP elements
There are a number of BuiltInLogicsheets
XSPCachingWithCocoonHEAD -- How to make XSPs cache when using Cocoon HEAD and version 2.1 and above - MilesElam
XSPActions -- How to write new Actions using XSP
XSPEnvironment -- Variables, helper classes, and default imports available in XSP
2.1 Documentation is missing? http://cocoon.apache.org/2.1/userdocs/generators/serverpages-generator.html