generate HTML5 by default exists and is marked done because we are now in a halfway-house where some HTML5 stuff (including the DTD) are emitted by default but most of the structural elements are not used and we have div soup. This page is a bug to request that we really move to HTML5 by default, specifically as a precursor to removing all the branching around this parameter that exists in the templates. Once the HTML5-by-default situation is settled, we could remove all that branching and then address generating HTML4.1 (or whatever) via a post-process DOM transformation plugin.
It's been 10 years since the HTML5 option was added. At the time there was some concern about legacy support for IE8. I rather suspect that the number of IE8 ikiwiki users (or ikiwiki users concerned about IE8) approximates zero, today. But if not, perhaps we should ?clarify what browser support is important for IkiWiki.
— Jon, 2020-12-30