A big part of verifying a design is checking its registers. A register packages is usually used to accomplish this task. It provides an abstract way of describing registers, their fields and their specific access policies, reset values, etc. For Specman, the vr_ad package is the most widespread.
This is a companion discussion topic for the original entry at https://verificationgentleman.netlify.app/2014/03/31/custom-field-access-policies-in-vrad.html