Clause library items can be setup to prompt for variable information that the user will be asked to enter as they are inserting the clause into a document. For example, it would be common to have skeleton signature or execution blocks set up in your clause library. For a company Common Seal execution block you might have this:

You can go further though. Rather than set the clause up with place markers that the user has to manually scan for (such as those yellow ones shown above), you can make I-Deal Docs automatically popup a small data entry window asking for the company details.