--- a/lib/common.inc.php
+++ b/lib/common.inc.php
@@ -113,9 +113,28 @@
 function include_header($title) {
     global $start;
     ?>
-    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"  
-        "http://www.w3.org/TR/html4/strict.dtd"> 
-    <html>
+    <!DOCTYPE html>
+    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" version="XHTML+RDFa 1.1"
+       xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+       xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
+       xmlns:gr="http://purl.org/goodrelations/v1#"
+       xmlns:dc="http://purl.org/dc/terms/"
+       xmlns:pc="http://purl.org/procurement#"
+       xmlns:unspsc="http://www.ksl.stanford.edu/projects/DAML/UNSPSC.daml#"
+       xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
+       xmlns:pcdt="http://purl.org/procurement/public-contracts-datatypes#"
+        prefix="rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns# 
+              rdfs: http://www.w3.org/2000/01/rdf-schema# 
+              gr: http://purl.org/goodrelations/v1# 
+              dcterms: http://purl.org/dc/terms/ 
+              pc: http://purl.org/procurement/public-contracts# 
+              cpv: http://purl.org/weso/pscs/cpv/2008/resource/ 
+              unspsc: http://www.ksl.stanford.edu/projects/DAML/UNSPSC.daml#
+              v: http://www.w3.org/2006/vcard/ns# 
+              payment: http://reference.data.gov.uk/def/payment# 
+              br: http://purl.org/business-register#              
+              xsd: http://www.w3.org/2001/XMLSchema# 
+              pcdt: http://purl.org/procurement/public-contracts-datatypes#">
         <head>
             <title><?php echo $title; ?> - Contract Dashboard</title>
             <link rel="stylesheet" type="text/css" href="bootstrap.min.css"> 

