def _header(title=""):
    """HTML page header."""
    if title:
        title = " - " + title
    header = """\
<html>
    <head>
        <title>Chaste Tests%s</title>
        <link rel="stylesheet" href="/style.css" type="text/css">
    </head>
    <body>
    <script type="text/javascript">
<!--
        function toggle_visibility(id) {
           var e = document.getElementById(id);
           if(e.style.display == 'block')
              e.style.display = 'none';
           else
              e.style.display = 'block';
        }
//-->
</script>
""" % title
    return header