use strict;
use warnings;
use 5.016;
use XML::LibXML;


my $dom = XML::LibXML->load_xml(string => <<'END_OF_XML');
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" 
     xmlns:xlink="http://www.w3.org/1999/xlink" 
     version="1.1">    
  <tag> 
    <text>
      <tspan>Hello</tspan>
    </text>
  </tag>
</svg>
END_OF_XML

#Deal with the namespace declared in the svg tag:

my $xpc = XML::LibXML::XPathContext->new($dom); 
$xpc->registerNs('ns', 'http://www.w3.org/2000/svg');
my ($tspan) = $xpc->findnodes('//ns:text/ns:tspan');

#Change the tspan's text:

$tspan->removeChildNodes();
$tspan->appendTextNode("Goodbye");

#Prove that the tspan's text changed:

say $tspan; 
say $dom->toString;