For this specification to be advanced to Proposed Recommendation, there must be at least two independent, interoperable implementations of each feature. Each feature may be implemented by a different set of products, there is no requirement that all features be implemented by a single product. For the purposes of this criterion, we define the following terms:
Each implementation must be developed by a different party and cannot share, reuse, or derive from code used by another qualifying implementation. Sections of code that have no bearing on the implementation of this specification are exempt from this requirement.
Qualitatively interoperable at at a judgment level, not necessarily for every spec assertion. A test suite may be used as guidance for the qualitative decision.
A user agent which: (1) implements the "Web browsers and other interactive user agents" conformance class of the specification. (2) is available to the general public. The implementation may be a shipping product or other publicly available version (i.e., beta version, preview release, or “nightly build”). Non-shipping product releases must have implemented the feature(s) for a period of at least one month in order to demonstrate stability, or be endorsed by their responsible organization as sufficiently stable. (3) is not experimental (i.e., a version specifically designed to pass the test suite and is not intended for normal usage going forward). (4) is suitable for a person to use as his/her primary means of accessing the Web.
For features that are well known to be widely implemented and deployed, and where implementations are believed to match the specification, the Working Group will assume effective real-world interoperability without testing. For features that are known not to be implemented at all, or unlikely to have multiple implementations during the CR period, the Working Group will not invest significant effort in testing. For features where the interoperability level is uncertain, the Working Group will create a sufficient test suite to make a judgment call; 100% pass rate will not necessarily be required. In any case where the judgment is debatable, it will be a Working Group decision whether sufficient interoperability has been achieved.
The specification will remain in Candidate Recommendation for at least six months.
A list of features at risk is being captured on the HTML WG Wiki.