Advisory Opinions in USPAP are best described as:

Advisory Opinions in USPAP (Uniform Standards of Professional Appraisal Practice) serve as guidance and clarification regarding the application of the standards in specific situations. They are not mandatory guidelines nor regulations; rather, they provide appraisers with insights and interpretations of USPAP to assist in understanding how to apply the standards effectively.

Since Advisory Opinions are designed to provide clarification and not bind appraisers to specific actions, they are indeed included as reference material. They help in understanding best practices and the intent behind various USPAP rules, but they do not impose legal requirements or compel appraisers to follow them strictly in their work. This context is important as it highlights that these opinions serve a supportive educational role rather than a regulatory one.