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+# RFC 215: Defining the Scope of web-platform-tests
+
+### Summary
+
+Define the scope of web-platform-tests to specifications which might reasonably be called "web specifications"
+and which are intended to be implemented by web browsers.
+
+Additionally, define what "tentative" might reasonably be used for.
+
+This is intended to codify existing practice,
+rather than represent any change.
+
+
+### Details
+
+Historically, what's been in scope for web-platform-tests has been somewhat nebulous,
+and largely based on a common understanding of participants,
+especially those on the Core Team.
+We should put this on surer footing,
+and make it easier for others to understand what is and isn't reasonable to add.
+
+The primary aim of web-platform-tests is to test
+[web specifications](https://github.com/w3c/browser-specs/blob/11a71b738f5e41f9239fdcd2074153388c8c6b8b/README.md#spec-selection-criteria)
+[intended to be implemented by browsers](https://github.com/w3c/browser-specs/blob/11a71b738f5e41f9239fdcd2074153388c8c6b8b/README.md#categories),
+both RFC 2119 "must" and RFC 2119 "should"
+implementation requirements.
+
+A specification does not need to have cross-vendor support for its tests to be included in web-platform-tests.
+(XXX: Should we set a bar of one-vendor support or are we okay with zero-vendor support?)
+
+Additionally, other features can be added as
+[tentative](https://web-platform-tests.org/writing-tests/file-names.html#:~:text=.tentative,-%3A%20)
+tests:
+
+ * Web browser behavior currently being explored via an
+   [explainer](https://tag.w3.org/explainers/),
+   but without a specification yet written.
+   (XXX: require prototyping to have started?)
+
+ * Historic but unspecified features in web browsers,
+   especially where major browsers are interoperable,
+   where there exists a long-term intention to specify them.
+   (Note: this excludes features which have been deliberately removed from specifications.
+    These are explicitly out of scope.)
+
+Features which are optional 
+(in RFC 2119 terms:
+ where the conformance criteria is
+ "may" or "may not")
+may be included as
+[optional tests](https://web-platform-tests.org/writing-tests/file-names.html#:~:text=.optional,-%3A%20)
+or
+[optional subtests](https://web-platform-tests.org/writing-tests/testharness-api.html#optional-features).
+
+
+### Risks
+
+We over-constrain what is allowed in web-platform-tests,
+potentially raising the bar to change what is allowed to "submit a new RFC",
+leading browser vendors to reduce what they submit to the project.