code: @Nonnull
    public final Schema getSchema (@Nonnull @Nonempty final IReadableResource... aResources)
    {
      ValueEnforcer.notEmptyNoNullValue (aResources, "Resources");
  
      return getFromCache (new CommonsArrayList <> (aResources));
    }
docs: Get a cached {@link Schema} that consists of multiple resources.
  
  @param aResources
  The resources to parse into a single {@link Schema}. May neither
  <code>null</code> nor empty nor may it contain <code>null</code>
  elements.
  @return Either the {@link Schema} from the cache or the newly compiled one.