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Some Working Groups define API definitions, with examples and are still using the W3C document license.
If you include WebIDL definitions, examples, code samples, the document license states (as of February 1st, 2015):
In addition, "Code Components" — Web IDL in sections clearly marked as Web IDL; and W3C-defined markup (HTML, CSS, etc.) and computer programming language code clearly marked as code examples— are licensed under the W3C Software License.
The W3C Software License is listed at the Open Source Initiative.