gitweb: switch to an XHTML5 DOCTYPE
According to the HTML Standard FAQ: “What is the DOCTYPE for modern HTML documents? In text/html documents: <!DOCTYPE html> In documents delivered with an XML media type: no DOCTYPE is required and its use is generally unnecessary. However, you may use one if you want (see the following question). Note that the above is well-formed XML.” Source: [1] Gitweb uses an XHTML 1.0 DOCTYPE: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> While that DOCTYPE is still valid [2], it has several disadvantages: 1. It’s misleading. If an XML parser uses the DTD at the given link, then the entities and ⋅ won’t get declared. Instead, the parser has to use a DTD from the HTML Standard that has nothing to do with XHTML 1.0 [2]. 2. It’s obsolete. XHTML 1.0 was last revised in 2002 and was superseded in 2018 [3]. 3. It’s unreliable. Gitweb uses and ⋅ but lets an external file define them. “[…U]using entity references for characters in XML documents is unsafe if they are defined in an external file (except for <, >, &, ", and ').” [4] [1]: <https://github.com/whatwg/html/blob/main/FAQ.md#what-is-the-doctype-for-modern-html-documents> [2]: <https://html.spec.whatwg.org/multipage/xhtml.html#parsing-xhtml-documents> [3]: <https://www.w3.org/TR/xhtml1/#xhtml> [4]: <https://html.spec.whatwg.org/multipage/xhtml.html#writing-xhtml-documents> Signed-off-by: Jason Yundt <jason@jasonyundt.email> Signed-off-by: Junio C Hamano <gitster@pobox.com>