+* change the doctype to `<!DOCTYPE html>`
+ unconditionally, stop trying to limit ourselves to XHTML 1.0 Strict
+ (use HTML5 features that degrade gracefully, like
+ [[ARIA roles|todo/add aria landmarks to make ikiwiki websites more accessible]]),
+ but avoid using the new elements like `<section>` that require specific
+ browser support unless `html5` is set to 1. That would get rid of the
+ backwards-compatibility concerns while keeping the ability to use
+ post-2000 markup; we can use `html5` to mean "be more enthusiastic about
+ HTML5 features even if they might fail on older browsers".
+
+Using the HTML5 doctype does mean we lose the ability to validate the output
+against a DTD (as `wdg-html-validator` does), but DTDs have very little to
+do with practical browser compatibility in any case.