diff --git a/Markdown.pl b/Markdown.pl
index f86763f..8999faa 100755
--- a/Markdown.pl
+++ b/Markdown.pl
@@ -2245,6 +2245,76 @@ sub _DoTag {
 }
 
 
+my %univatt;	# universally allowed attribute names
+my %tagatt;	# per-element allowed attribute names
+my %tagmt;	# empty element tags
+my %tagocl;	# non-empty elements with optional closing tag
+my %tagacl;	# which %tagocl an opening %tagocl will close
+my %tagblk;	# block elements
+my %lcattval;	# names of attribute values to lowercase
+my %impatt;	# names of "implied" attributes
+BEGIN {
+    %univatt = map({$_ => 1} qw(class dir id lang style title xml:lang));
+    %tagatt = (
+	'a' => { map({$_ => 1} qw(href name)) },
+	'area' => { map({$_ => 1} qw(alt coords href nohref shape)) },
+	'basefont' => { map({$_ => 1} qw(color face size)) },
+	'br' => { map({$_ => 1} qw(clear)) },
+	'caption' => { map({$_ => 1} qw(align)) },
+	'col' => { map({$_ => 1} qw(align span width valign)) },
+	'colgroup' => { map({$_ => 1} qw(align span width valign)) },
+	'dir' => { map({$_ => 1} qw(compact)) },
+	'div' => { map({$_ => 1} qw(align)) },
+	'dl' => { map({$_ => 1} qw(compact)) },
+	'font' => { map({$_ => 1} qw(color face size)) },
+	'h1' => { map({$_ => 1} qw(align)) },
+	'h2' => { map({$_ => 1} qw(align)) },
+	'h3' => { map({$_ => 1} qw(align)) },
+	'h4' => { map({$_ => 1} qw(align)) },
+	'h5' => { map({$_ => 1} qw(align)) },
+	'h6' => { map({$_ => 1} qw(align)) },
+	'hr' => { map({$_ => 1} qw(align noshade size width)) },
+	# NO server-side image maps, therefore NOT ismap !
+	'img' => { map({$_ => 1} qw(align alt border height hspace src usemap vspace width)) },
+	'li' => { map({$_ => 1} qw(compact type value)) },
+	'map' => { map({$_ => 1} qw(name)) },
+	'menu' => { map({$_ => 1} qw(compact)) },
+	'ol' => { map({$_ => 1} qw(compact start type)) },
+	'p' => { map({$_ => 1} qw(align)) },
+	'pre' => { map({$_ => 1} qw(width)) },
+	'table' => { map({$_ => 1} qw(align border cellpadding cellspacing summary width)) },
+	'tbody' => { map({$_ => 1} qw(align valign)) },
+	'tfoot' => { map({$_ => 1} qw(align valign)) },
+	'thead' => { map({$_ => 1} qw(align valign)) },
+	'td' => { map({$_ => 1} qw(align colspan height nowrap rowspan valign width)) },
+	'th' => { map({$_ => 1} qw(align colspan height nowrap rowspan valign width)) },
+	'tr' => { map({$_ => 1} qw(align valign)) },
+	'ul' => { map({$_ => 1} qw(compact type)) }
+    );
+    %tagmt = map({$_ => 1} qw(area basefont br col hr img));
+    %tagocl = map({$_ => 1} qw(colgroup dd dt li p tbody td tfoot th thead tr));
+    %tagacl = (
+	'colgroup' => \%tagocl,
+	'dd' => \%tagocl,
+	'dt' => \%tagocl,
+	'li' => \%tagocl,
+	'tbody' => \%tagocl,
+	'td' => { map({$_ => 1} qw(colgroup dd dt li p td tfoot th thead)) },
+	'tfoot' => \%tagocl,
+	'th' => { map({$_ => 1} qw(colgroup dd dt li p td tfoot th thead)) },
+	'thead' => \%tagocl,
+	'tr' => { map({$_ => 1} qw(colgroup dd dt li p td tfoot th thead tr)) },
+    );
+    %tagblk = map({$_ => 1} qw(address blockquote div dl h1 h2 h3 h4 h5 h6 hr ol p pre table));
+    %impatt = map({$_ => 1} qw(checked compact ismap nohref noshade nowrap));
+    %lcattval = map({$_ => 1} qw(
+	align border cellpadding cellspacing checked clear color colspan
+	compact coords height hspace ismap nohref noshade nowrap rowspan size
+	span shape valign vspace width
+    ));
+}
+
+
 # _SanitizeTags
 #
 # Inspect all '<'...'>' tags in the input and HTML encode those things
@@ -2254,13 +2324,37 @@ sub _DoTag {
 # <= sanitized text
 sub _SanitizeTags {
     my ($text, $validate) = @_;
+    $text =~ s/\s+$//;
+    $text ne "" or return "";
     my @stack = ();
     my $ans = "";
     my $end = length($text);
     pos($text) = 0;
+    my ($autoclose, $autoclopen);
+    my $lastmt = "";
+    $autoclose = sub {
+	my $s = $_[0] || "";
+	while (@stack && $stack[$#stack]->[0] ne $s &&
+		$tagocl{$stack[$#stack]->[0]}) {
+	    $ans .= "</" . $stack[$#stack]->[0] . ">";
+	    pop(@stack);
+	}
+    } if $validate;
+    $autoclopen = sub {
+	my $s = $_[0] || "";
+	my $c;
+	if ($tagblk{$s}) {$c = {p=>1}}
+	elsif ($tagocl{$s}) {$c = $tagacl{$s}}
+	else {return}
+	while (@stack && $c->{$stack[$#stack]->[0]}) {
+	    $ans .= "</" . $stack[$#stack]->[0] . ">";
+	    pop(@stack);
+	}
+    } if $validate;
     while (pos($text) < $end) {
 	if ($text =~ /\G([^<]+)/gc) {
 	    $ans .= $1;
+	    $lastmt = "" if $1 =~ /\S/;
 	    next;
 	}
 	my $tstart = pos($text);
@@ -2270,17 +2364,23 @@ sub _SanitizeTags {
 		$ans .= $tag;
 		next;
 	    }
+	    my $tt;
 	    if (($tag =~ m{^<($g_possible_tag_name)(?:[\s>]|/>$)} ||
 		 $tag =~ m{^</($g_possible_tag_name)\s*>}) &&
-		$ok_tag_name{lc($1)})
+		$ok_tag_name{$tt=lc($1)})
 	    {
 		my ($stag, $styp) = _Sanitize($tag);
-		$ans .= $stag;
-		if ($validate && ($styp == 1 || $styp == 2) && $stag =~ m{^</?([^/\s>]+)}) {
-		    my $tt = $1;
+		if ($styp == 2 && $lastmt eq $tt) {
+		    $lastmt = "";
+		    next;
+		}
+		$lastmt = $styp == 3 ? $tt : "";
+		if ($validate && $styp) {
+		    &$autoclopen($tt) if $styp == 1 || $styp == 3;
 		    if ($styp == 1) {
 			push(@stack,[$tt,$tstart]);
-		    } else {
+		    } elsif ($styp == 2) {
+			&$autoclose($tt) unless $tt eq "p";
 			!@stack and _xmlfail("closing tag $tt without matching open at " .
 			    _linecol($tstart, $text));
 			if ($stack[$#stack]->[0] eq $tt) {
@@ -2292,28 +2392,32 @@ sub _SanitizeTags {
 			}
 		    }
 		}
+		$ans .= $stag;
 		next;
 	    } else {
 		$tag =~ s/^</&lt;/;
 		$ans .= $tag;
+		$lastmt = "";
 		next;
 	    }
 	}
 	# can only get here if "\G" char is an unmatched "<"
 	pos($text) += 1;
 	$ans .= "&lt;";
+	$lastmt = "";
     }
+    &$autoclose if $validate;
     if ($validate && @stack) {
 	my @errs;
 	my $j;
 	for ($j = 0; $j <= $#stack; ++$j) {
 		my @i = @{$stack[$j]};
-		push(@errs, "opening tag $i[0] without matching close at " .
+		unshift(@errs, "opening tag $i[0] without matching close at " .
 			    _linecol($i[1], $text));
 	}
 	_xmlfail(@errs);
     }
-    return $ans;
+    return $ans."\n";
 }
 
 
@@ -2332,59 +2436,6 @@ sub _xmlfail {
 }
 
 
-my %univatt;	# universally allowed attribute names
-my %tagatt;	# per-element allowed attribute names
-my %tagmt;	# empty element tags
-my %lcattval;	# names of attribute values to lowercase
-my %impatt;	# names of "implied" attributes
-BEGIN {
-    %univatt = map({$_ => 1} qw(class dir id lang style title xml:lang));
-    %tagatt = (
-	'a' => { map({$_ => 1} qw(href name)) },
-	'area' => { map({$_ => 1} qw(alt coords href nohref shape)) },
-	'basefont' => { map({$_ => 1} qw(color face size)) },
-	'br' => { map({$_ => 1} qw(clear)) },
-	'caption' => { map({$_ => 1} qw(align)) },
-	'col' => { map({$_ => 1} qw(align span width valign)) },
-	'colgroup' => { map({$_ => 1} qw(align span width valign)) },
-	'dir' => { map({$_ => 1} qw(compact)) },
-	'div' => { map({$_ => 1} qw(align)) },
-	'dl' => { map({$_ => 1} qw(compact)) },
-	'font' => { map({$_ => 1} qw(color face size)) },
-	'h1' => { map({$_ => 1} qw(align)) },
-	'h2' => { map({$_ => 1} qw(align)) },
-	'h3' => { map({$_ => 1} qw(align)) },
-	'h4' => { map({$_ => 1} qw(align)) },
-	'h5' => { map({$_ => 1} qw(align)) },
-	'h6' => { map({$_ => 1} qw(align)) },
-	'hr' => { map({$_ => 1} qw(align noshade size width)) },
-	# NO server-side image maps, therefore NOT ismap !
-	'img' => { map({$_ => 1} qw(align alt border height hspace src usemap vspace width)) },
-	'li' => { map({$_ => 1} qw(compact type value)) },
-	'map' => { map({$_ => 1} qw(name)) },
-	'menu' => { map({$_ => 1} qw(compact)) },
-	'ol' => { map({$_ => 1} qw(compact start type)) },
-	'p' => { map({$_ => 1} qw(align)) },
-	'pre' => { map({$_ => 1} qw(width)) },
-	'table' => { map({$_ => 1} qw(align border cellpadding cellspacing summary width)) },
-	'tbody' => { map({$_ => 1} qw(align valign)) },
-	'tfoot' => { map({$_ => 1} qw(align valign)) },
-	'thead' => { map({$_ => 1} qw(align valign)) },
-	'td' => { map({$_ => 1} qw(align colspan height nowrap rowspan valign width)) },
-	'th' => { map({$_ => 1} qw(align colspan height nowrap rowspan valign width)) },
-	'tr' => { map({$_ => 1} qw(align valign)) },
-	'ul' => { map({$_ => 1} qw(compact type)) }
-    );
-    %tagmt = map({$_ => 1} qw(area basefont br col hr img));
-    %impatt = map({$_ => 1} qw(checked compact ismap nohref noshade nowrap));
-    %lcattval = map({$_ => 1} qw(
-	align border cellpadding cellspacing checked clear color colspan
-	compact coords height hspace ismap nohref noshade nowrap rowspan size
-	span shape valign vspace width
-    ));
-}
-
-
 sub _Sanitize {
     my $tag = shift;
     my $seenatt = {};
@@ -3057,15 +3108,20 @@ to be recognized and passed through even without using this option.
 
 =item B<--sanitize>
 
-Remove troublesome tag attributes from embedded tags.  Only a very strictly
+Removes troublesome tag attributes from embedded tags.  Only a very strictly
 limited set of tag attributes will be permitted, other attributes will be
 silently discarded.  The set of allowed attributes varies by tag.
-This is enabled by default.
 
-Also split empty minimized elements that are not one of the HTML allowed
-empty elements (C<area> C<basefont> C<br> C<col> C<hr> C<img>) into separate
-begin and end tags.  For example, C<< <p/> >> or C<< <p /> >> will be split
-into C<< <p></p> >>.
+Splits empty minimized elements that are not one of the HTML allowed empty
+elements (C<area> C<basefont> C<br> C<col> C<hr> C<img>) into separate begin
+and end tags.  For example, C<< <p/> >> or C<< <p /> >> will be split into
+C<< <p></p> >>.
+
+Combines adjacent (whitespace separated only) opening and closing tags for
+the same HTML empty element into a single minimized tag.  For example,
+C<< <br></br> >> will become C<< <br /> >>.
+
+This is enabled by default.
 
 
 =item B<--no-sanitize>
@@ -3086,8 +3142,8 @@ module be present (one is only required if this option is given).
 
 Any errors are reported to STDERR and the exit status will be
 non-zero on XML validation failure.  Note that all line and column
-numbers in the output refer to the entire output that would have
-been produced.  Re-run with B<--no-validate-xml> to see what's
+numbers in the error output refer to the entire output that would
+have been produced.  Re-run with B<--no-validate-xml> to see what's
 actually present at those line and column positions.
 
 If the B<--stub> option has also been given, then the entire output is
@@ -3107,13 +3163,19 @@ Perform XML validation on the output before it's output and die if
 it fails validation.  This uses a simple internal consistency checker
 that finds unmatched and mismatched open/close tags.
 
+Non-empty elements that in HTML have optional closing tags (C<colgroup>
+C<dd> C<dt> C<li> C<p> C<tbody> C<td> C<tfoot> C<th> C<thead> C<tr>)
+will automatically have any omitted end tags inserted during the
+`--validate-xml-internal` process.
+
 Any errors are reported to STDERR and the exit status will be
 non-zero on XML validation failure.  Note that all line and column
-numbers in the output refer to the entire output that would have
-been produced without any B<--stub> or B<--stylesheet> options.
-Re-run with B<--no-validate-xml> and I<without> any B<--stub> or
-B<--stylesheet> options to see what's actually present at those
-line and column positions.
+numbers in the error output refer to the entire output that would
+have been produced before sanitization without any B<--stub> or
+B<--stylesheet> options.  Re-run with B<--no-sanitize> and
+B<--no-validate-xml> and I<without> any B<--stub> or B<--stylesheet>
+options to see what's actually present at those line and column
+positions.
 
 This option validates the output I<prior to> adding any requested
 B<--stub> or B<--stylesheet>.  As the built-in stub and stylesheet