Current information about building and using pkg-plugins

[John Wolfe]

Where does one find the information about building and using pkg-plugins.

The source on github.com://freebsd/pkg-plugins is approximately 2 years 
old.   Is there something more current?

Will such a plugin work with pkg version 1.3.8 and 1.4.x or are plugins 
tightly couple to the version of pkg on ones system?

Thanks in advance for any pointers.

-- John