How can I add a user directive to Polaris' vocabulary?

NOTE: This question is intended for developers of Polaris.

For simplicity, assume you would like to add a directive of the form:

    CSRD$ VARRANGE var,lb,ub
With this directive, you intend for users to be able to indicate the range a variable can have, i.e., lb <= var <= ub.

Files you will have to create:

Files you will have to modify: