JBoss Tools introduced JSF 2 Composite Component support in version 3.2.0.M1, it matured through several development versions and got a lot of useful features:

1. Content assist for component developers
2. Content assist for component users
3. Validation and quick fixes
4. Refactoring
5. Rendering in XHTML Visual Editor
6. Resource Navigation in source and visual part of XHTML Visual Editor

Read full article about JBoss Tools JSF 2 Composite Component Support.