The goal of this document is to help W3C editors write better specifications, by making a specification easier to interpret without ambiguity and clearer as to what is required in order to conform. It focuses on how to define and specify conformance. It also addresses how a specification might allow variation among conforming implementations. The document presents guidelines or requirements, supplemented with good practices, examples and techniques.
CSS3 Backgrounds and Borders Test Suite, NISTGCR, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=150537, http://xsun.sdct.itl.nist.gov/~boland/css3/spec/index1.html
(Accessed May 31, 2023)