There are a few ways to limit values. The method is application dependent.
The 1st that comes to mind is dragging components that have assembly constraints. These will have degrees of freedom within their specified constraint limits.
Second is the ability to use "if" statements in relations where you can have set allowable or ranges of valid values.
If you have an "if/then" type of evaluation, you can use a graph feature drive your relation. If X=n then Y=value of graph.
If you have a better idea of exactly your coworker is trying to accomplish, we can dive deeper into any of these.