We no longer have a test for DTD-valid XHTML 1.0, but at least check well-formedness

This means that people can do XSLT nonsense if they want to.

The failures are currently marked TODO because not everything in the
docwiki is in fact well-formed.

t/wellformed.t

@@ -0,0 +1,50 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+use Cwd qw();
+use File::Find;
+use Test::More;
+
+plan(skip_all => "XML::Parser not available")
+	unless eval q{use XML::Parser (); 1;};
+
+use IkiWiki;
+
+ok(system("make >/dev/null") == 0);
+
+chdir("html") || die "chdir: $!";
+
+sub wanted {
+	my $file = $_;
+	return if -d $file;
+	$file =~ s{^\./}{};
+	return if $file !~ m/\.html$/;
+	if (eval {
+		XML::Parser->new()->parsefile($file);
+		1;
+	}) {
+		pass($file);
+	}
+	elsif ($file =~ m{^(?:
+			# user-contributed, contains explicit <br>
+			plugins/contrib/gallery |
+			# use templatebody when branchable.com has been upgraded
+			templates/ |
+			# malformed content in <pre> not escaped by discount
+			tips/convert_mediawiki_to_ikiwiki
+			# user-contributed, content is anyone's guess
+			users/ |
+			)}x) {
+		TODO: {
+			local $TODO = $@;
+			fail($file);
+		}
+	}
+}
+
+find({
+	no_chdir => 1,
+	wanted => \&wanted,
+}, '.');
+
+done_testing;