This project uses GIT to manage its source code. Instructions on GIT use can be found at http://git-scm.com/documentation.
The source can be checked out anonymously from GIT with this command (See http://git-scm.com/docs/git-clone):
$ git clone https://git-wip-us.apache.org/repos/asf/maven.git/maven-plugin-api
Only project developers can access the GIT tree via this method (See http://git-scm.com/docs/git-clone).
$ git clone https://git-wip-us.apache.org/repos/asf/maven.git/maven-plugin-api