Added a bullet on versioning.

docs/projections.md

@@ -9,6 +9,7 @@ Below are some principles that all language projections should follow:
 * Language projections should provide maximum API coverage
 * Language projections should provide friendly adaptations of APIs and types where appropriate
 * Language projections should provide Intellisense sourced from official documentation
+* Language projections should support filtering available APIs based on the SDK version that a project targets
 * Language projections should enable developers to target a specific set of APIs and link or include only the artifacts necessary to provide support for those APIs
 
 ## Projections