What has changed with <meta name="robots" content="index,follow"> meta tag? I use HTML5 and W3C validator marks my page as invalid. There is robots meta name allowed in http://wiki.whatwg.org/wiki/MetaExtensions.
Exact validator error:
Bad value
robotsfor attributenameon elementmeta: Keywordrobotsis not registered.
unor
The validator is wrong.
The robots name is registered according to HTML5’s rules, so you can use it.
You’ll probably see the same problem with all other registered names, too (e.g., with the google name).
来源：https://stackoverflow.com/questions/22100619/w3c-validator-bad-value-robots-for-attribute-name-on-element-meta