+unless (defined $doc) {
+ print "The link to this page was broken - it must specify a .txt file.";
+ exit;
+}
+
+# Prevent hackers from supplying a malformed document string.
+# I.e. only allow normal characters, slashes and dots.
+unless ($doc =~ /^[a-zA-Z_\-0-9\.\/]+$/) {
+ print "Malformed request";
+ exit;
+}
+$doc = "../htdocs/documentation/".$doc;
+