--- a/es/screenshots.xml
+++ b/es/screenshots.xml
@@ -1,7 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?xml-stylesheet type="text/xsl" href="../main.xsl"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml" id="screenshots" xml:lang="es">
-<head><title>Algunas capturas de pantalla</title></head>
+<head>
+    <title>Algunas capturas de pantalla</title>
+    <link rel="schema.DC" href="http://purl.org/dc/elements/1.1/"/>
+    <link rel="schema.DCTERMS" href="http://purl.org/dc/terms/"/>
+    <meta name="DC.identifier" scheme="DCTERMS.URI" content="http://maxima.sourceforge.net/es/screenshots.html"/>
+</head>
 <body>
 <p class="labeled-image"><img src="../i/xmaximalinux.png" alt=""/><br/>
 Xmaxima corriendo en Linux</p>