code: @CheckForNull
      public Descriptor getDescriptor(Class<? extends Describable> type) {
          for( Descriptor d : getExtensionList(Descriptor.class) )
              if(d.clazz==type)
                  return d;
          return null;
      }
docs: Gets the {@link Descriptor} that corresponds to the given {@link Describable} type.
  <p>
  If you have an instance of {@code type} and call {@link Describable#getDescriptor()},
  you'll get the same instance that this method returns.