code: @Nonnull
    @OverrideOnDemand
    public PSSchema readSchema (@Nonnull final IReadableResource aResource,
                                @Nullable final IPSErrorHandler aErrorHandler,
                                @Nullable final EntityResolver aEntityResolver) throws SchematronException
    {
      return new PSReader (aResource, aErrorHandler, aEntityResolver).readSchema ();
    }
docs: Read the specified schema from the passed resource.
  
  @param aResource
  The resource to read from. Never <code>null</code>.
  @param aErrorHandler
  The error handler to use. May be <code>null</code>.
  @param aEntityResolver
  The XML entity resolver to be used. May be <code>null</code>.
  @return The read schema. May not be <code>null</code>.
  @throws SchematronException
  In case there is an error reading.