The MyFaces Core is the portion of MyFaces that implements the JSF Specification. The specification includes both an API and an Implementation aspect and the MyFaces API and MyFaces Impl subprojects mirror this concept.
To use the MyFaces implementation you will need to download one of the core release versions. Each version XXX of the core that is released will contain myfaces-api-XXX.jar and myfaces-impl-XXX.jar.
NOTE: The version of commons is not necessarily the same as the version of the api and impl. All three jar files must be in your classpath in order to use the MyFaces JSF implementation.
NOTE: This newly bundled core is not yet available as an official release. For now it can be build using Maven or obtained through the nightly build link.
JSR-127: JavaServer Faces
MyFaces currently implements Java Specification Request 127. Each release is certified against the Sun TCK to ensure compliance.
JSR-252: JavaServer Faces 1.2
There is a new JSR, Java Specification Request 252, which includes several major improvements to JSF. The specification is currently in Proposed Final Draft form. There are no immediate plans to implement this specification in MyFaces but it is likely that work will begin once the spec is finalized.