Another example for this would be to check if an input title is contained in a list which itself is saved in a variable, I think. The other way around would simply use match<title> to check if the title stored in is contained in the input list. I believe the current solution for this is :filter, together with enlist[] and match[], which performs the enlisting for each input title, which is probably not very efficient.
This is something I run across every now and then, since I usally save the results of the more expensive operations like search:*[] into variables to keep things running smoothly…