In future-V7 you can write custom DRC rules with assertions: Post-v6 new features and development news - #27 by JeffYoung
You would use an assertion for something that you think will always be true, but you want an error if it’s not. For example you could assert that a particular constraint is always set to a certain value. If it gets overridden in a way that you don’t expect, you’ll get a DRC error.
Ignore this if it is an unhelpful comparison, but this maps to the programming concept of an assertion, except you’re writing an assertion about your board design rather than a programmer writing an assertion about their code.