- This improves scroll snap behaviour
- Set background color of page
- Interpret the margin of a page as padding. What it really is

ImportModuleVersion stores the unitDefinitionType of the loaded unit
definition. During the initialization of the unit, the individual
elements can react to the stored value.

and DropListSimpleElement

Use singleton instance of IdService in UIElement

This is not a complete backwards compatibility. Only the value "0" can
be safely classified as false. It is therefore set to "1".

- Refactor findNestedUIElement as static class method