The Apache Flex project has two compiler source code bases. The MXMLC compiler code is in the flex-sdk repo in the modules folder. MXMLC is the compiler that ships with the Apache Flex SDK and is used to compile MXML and ActionScript into SWFs. A completely different repo is dedicated to a next-generation Flex compiler called Falcon, and a cross-compiler (also called a transpilar) called FalconJX. The Falcon and FalconJX code bases are intended to be framework-agnostic, and potentially have their own release schedule independent of the Flex and FlexJS SDKs someday. For now, they are released as an upstream dependency for the FlexJS SDK. They have not been certified against the regular Flex SDK.