use XML::Parser;
use strict;

use constant SVGNS => 'http://www.w3.org/2000/svg';
use constant XLINKNS => 'http://www.w3.org/1999/xlink';

sub xmlEscape {
  $_ = shift;
  s/&/&/g;
  s/</&lt;/g;
  s/>/&gt;/g;
  return $_;
}

sub xmlSerialize {
  my ($expat,$element,@attrs) = @_;
  $element = "svg:$element" if $expat->namespace($element) eq SVGNS;
  while (@attrs) {
    my ($name, $value) = (shift(@attrs), xmlEscape(shift(@attrs)));
    $name = "xlink:$name" if $expat->namespace($name) eq XLINKNS;
    $value =~ s/"/&quot;/g;
    $element .= " $name=\"$value\"";
  }
  return $element;
}

sub svgprefix {
  my $input = shift;
  my $output = '';
  my $parser = new XML::Parser(Namespaces => 1);
  $parser->setHandlers(
    Char  => sub {shift; $output .= xmlEscape(shift)},
    Start => sub {$output .= '<' . xmlSerialize(@_) . '>'},
    End   => sub {$output .= '</' . xmlSerialize(@_) . '>'},
  );
  eval {$parser->parse($input)} or return $input;
  $output =~ s/<svg:svg/$& xmlns:xlink="${\XLINKNS}"/g if $output =~ / xlink:/;
  $output =~ s/<svg:svg/$& xmlns:svg="${\SVGNS}"/g;
  return $output;
}

print svgprefix(<<EOX);
<div class="centeredfigure">
  <svg xmlns="http://www.w3.org/2000/svg"
       width="192" height="64" viewBox="0 0 120 40">
    <desc>sphere, cube, tetrahedron</desc>
    <defs>
      <radialGradient id="plat1" fx=".3" fy=".3" r=".7">
        <stop stop-color="#CCF" offset="0" />
        <stop stop-color="#55F" offset="1" />
      </radialGradient>
      <linearGradient id="squ1" x1=".3" y1=".3" x2="1.7" y2="1.7">
        <stop stop-color="#CDC" offset="0" />
        <stop stop-color="#6D6" offset="1" />
      </linearGradient>
      <linearGradient id="squ2" x1="0" y1="0" x2="1" y2="-.6" l:href="#squ1" xmlns:l="http://www.w3.org/1999/xlink" />
    </defs>
    <g transform="translate(5,5)" stroke="none">
      <circle cx="15" cy="15" r="15" fill="url(#plat1)" />
      <g stroke="#9D9" stroke-width=".5" stroke-opacity="0.6">
        <rect width="20" height="20" x="40" y="10" fill="url(#squ1)" />
        <path d="M 40 10 l 20   0 l 10 -10 l -20  0 z" fill="url(#squ2)" />
        <path d="M 60 30 l  0 -20 l 10 -10 l   0 20 z" fill="#9D9" />
      </g>
      <g>
        <path d="M 95 0 l -17 20 l  17 10 z" fill="#FCC" />
        <path d="M 95 0 l  17 20 l -17 10 z" fill="#FBB" />
      </g>
    </g>
  </svg><br />
  <span class="figurecaption">Three Solids</span>
</div>
EOX