code: @Nonnull
    @CheckReturnValue
    public CSSSimpleValueWithUnit add (@Nonnull final BigDecimal aDelta)
    {
      return new CSSSimpleValueWithUnit (m_aValue.add (aDelta), m_eUnit);
    }
docs: Get a new object with the same unit but an added value.
  
  @param aDelta
  The delta to be added. May not be <code>null</code>.
  @return A new object. Never <code>null</code>.
  @since 3.7.3