fixup!

index.bs

@@ -1164,7 +1164,7 @@ The following extended attributes are applicable to interfaces:
 </div>
 
 
-<h3 id="idl-mixins">Mixins</h3>
+<h3 id="idl-interface-mixins">Interface mixins</h3>
 
 An <dfn export>interface mixin</dfn> is a definition (matching <emu-t>interface</emu-t> <emu-nt><a href="#prod-MixinRest">MixinRest</a></emu-nt>)
 that declares state and behavior that can be [=included=] by one or more [=interfaces=],
@@ -1337,7 +1337,7 @@ No [=extended attributes=] defined in this specification are applicable to [=inc
         identifier "includes" identifier ";"
 </pre>
 
-<h4 id="using-mixins-and-partials">Using Mixins and Partials</h4>
+<h4 id="using-mixins-and-partials">Using mixins and partials</h4>
 
 <i>This section is informative.</i>