The active annotation is used to register compilation participants with annotations. They allow for enhancing and changing how Xtend code is translated to Java. There are four compiler phases in which an active annotation can participate, each with different possibilities and constraints:

• Phase 1: Register Globals RegisterGlobalsParticipant
• Phase 2: Transformation TransformationParticipant
• Phase 3: Validate Code ValidationParticipant
• Phase 4: Generate Code CodeGenerationParticipant

Note, that in the IDE phase one, two and three are executed in the editor as you type, while phase 4 (code generation) only gets executed when the editor's contents gets saved to disk.