let
 pkgs = import <nixpkgs> {};
 inherit (pkgs) emacsPackagesNg docbook5 writeText;

 schemas = writeText "schemas.xml" ''
   <locatingRules xmlns="http://thaiopensource.com/ns/locating-rules/1.0">
     <documentElement localName="section" typeId="DocBook"/>
     <documentElement localName="chapter" typeId="DocBook"/>
     <documentElement localName="article" typeId="DocBook"/>
     <documentElement localName="book" typeId="DocBook"/>
     <typeId id="DocBook" uri="${docbook5}/xml/rng/docbook/docbookxi.rnc" />
   </locatingRules>
 '';

in emacsPackagesNg.emacsWithPackages (epkgs: [
 (emacsPackagesNg.trivialBuild {
   pname = "nix-docbook-mode";
   version = "1970-01-01";
   src = writeText "default.el" ''
     (eval-after-load 'rng-loc
       '(add-to-list 'rng-schema-locating-files "${schemas}"))
     (global-set-key (kbd "<C-return>") 'nxml-complete)
   '';
 })
])