We have this example in our documentation https://docs.readthedocs.io/en/latest/build-customization.html#cancel-build-based-on-a-condition that mentions how to cancel a build based on a particular condition. This is a good example and we have more and more people using it.

However, it does not talk about the feature it self at all. We should probably create a completely new page for this feature and explain it in a more in-deep way. We can grab some ideas from "Netlify's ignore builds" documentation: https://docs.netlify.com/configure-builds/ignore-builds/