Bug#980921: Validation of HTML5

Package: www.debian.org
Followup-For: Bug #980921

When thinking about the migration, please also take into account the
effect of moving to HTML on the validation script.

I don't know whether I did it correctly, but for me simply replacing the
doctype with "html" caused the validation script to fail with:

*** Errors validating ../view-source_https___www.debian.org.html: ***
Line 1, character 15:  no internal or external document type declaration
	subset; will parse without validation
Line 51, character 24:	general entity "nbsp" not defined and no default
	entity
Line 51, character 28:	reference to entity "nbsp" for which no system
	identifier could be generated
Line 256, character 115:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 257, character 121:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 261, character 117:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 265, character 118:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 267, character 115:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 270, character 116:  reference to entity "nbsp" for which no system
	identifier could be generated
Line 272, character 118:  reference to entity "nbsp" for which no system
	identifier could be generated

I suppose this is because the validator is based on the DTDs in
/usr/share/sgml/html/... and there is none for HTML5 there?

-- System Information:
Debian Release: 10.8
  APT prefers stable-debug
  APT policy: (500, 'stable-debug'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-14-amd64 (SMP w/4 CPU cores)
Locale: LANG=pl_PL.UTF-8, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8), LANGUAGE=pl_PL.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled