XSL Tools/API Tooling
For developing the XSL Tools plugins, all XSL Tools committers and contributors should have a Base Line eclipse installation installed. XSL Tools plugins have PDE's API Tooling enabled to help catch API breakages and versioning errors.
Setup API Tooling
For information on setting up API tooling see the following article:
Eclipse 3.4 JEE package should be the base line along with XSL Tools 0.5 added to that package.
Make sure to set up your Base Line reference in the Prefences->Plugin-Development->API Base Line
The name should be WTP 3.0.