HTML validation will make it more likely that our code doesn't run into cross-browser issues. In order for this to be most useful, we need a clean slate, so we can easily see when new issues crop up.
The base href error in particular is apparently causing the validator to ignore certain errors ("Suppressing further errors from this subtree"). There is a duplicate attribute error at https://www.mediawiki.org/wiki/Talk:Flow_QA with both data-flow-api-handler="watchItem" and data-flow-api-handler="watchTopic". I'm not sure why, but the validator is not picking that up, even though it does pick up the same thing in a self-contained test case (which is otherwise valid).
The errors are:
- "Element base not allowed as child of element div in this context." (it's not allowed in the body)
- "Attribute name not allowed on element script at this point." for "<script name="handlebars-template-progressive-enhancement"" (never used, only the type is).
There are also some warnings:
- "Potentially bad value ... for attribute datetime on element time: Year may be mistyped." This is apparently because our time_iso is not actually ISO time; it is also not valid for this parameter. It seems that it should be an error, but the validator is going easy on us (possibly because it's confused with something else).