Rustbook has some errors when validating HTML

[azerupi]

I've tested html validation of the rust book with the W3C validator and there is only one error, but it is all over the place. There is one id that appears multiple times #rust-example-rendered. If it appears that often it should be a class not an id.

I have tested multiple pages randomly and it seems like the only error :)
So good job !

Link to validator