Microgrammars are “partial grammars designed to extract checker-specific features only”.
When there is no existing Rug extension and plain file manipulation is too clumsy and random, the microgrammar (pdf) support in Rug provides an effective way of declaring a way to safely select and extract a portion of a file so that it can be inspected and manipulated by your Rugs.
For more on microgrammars we recommend you check out this post by Adrian Colyer.
The Atomist implementation of microgrammars is undergoing rapid
development and change. Please see
implementation for the latest documentation and usage.