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Validator incorrectly reports that opacity does not exist, but it is listed here in the specs: http://www.w3.org/TR/css3-color/#transparency This causes sites to fail validation even though their code is fully compliant - a problem for any designer who prides him or herself on standards compliance (one of my sites was listed among the 35 best built political sites out of 1000 tested by CNET for that very reason).
Hello all, opacity is a CSS 3 (color module) property. When submitting a webpage to CSS validator, the default profile is CSS 2.1 and not CSS 3 profile. Demonstration that opacity is correctly reported as valid property name when submitted to W3C CSS validator (with a CSS 3 profile): http://www.gtalbot.org/BugzillaSection/TestingOpacityCSSValidation.html In my opinion, this bug is INVALID
Indeed opacity is not in the default CSS2.1, but setting the validator to check against css3 works. The validator now gives a more user-friendly message when using css2.1: Property opacity doesn't exist in CSS level 2.1 but exists in [css3] I'm closing this as WORKSFORME