interfaces.xml Add enums to declarations shared a namespace with interfaces (#4150)

Author: mmalferov

language/oop5/interfaces.xml

@@ -5,7 +5,7 @@
   <para>
    Object interfaces allow you to create code which specifies which methods and properties a
    class must implement, without having to define how these methods or properties are
-   implemented.  Interfaces share a namespace with classes and traits, so they may
+   implemented.  Interfaces share a namespace with classes, traits, and enumerations, so they may
    not use the same name.
   </para>
   <para>