anchor.diff:  
   let
   
  -  common = { pname, sha256 }: let self = stdenv.mkDerivation rec {
  +  common = { pname, sha256, patches ? [] }: let self = stdenv.mkDerivation rec {
       name = "${pname}-1.79.1";
   
       src = fetchurl {
  
positive.code:   docbook_xsl = common {
      pname = "docbook-xsl";
      sha256 = "0s59lihif2fr7rznckxr2kfyrvkirv76r1zvidp9b5mj28p4apvj";
    };
  
    docbook_xsl_ns = common {
  
negative.code:       inherit sha256;
      };
  
      inherit patches;
  
      propagatedBuildInputs = [ findXMLCatalogs ];
  
  