This allows to select elements without clicking them on the canvas, as 
elements may be obstructed or not visible for some reason.

The selection logic is a bit complicated because usually only the 
overlay components are usd for selection which are also the place to 
apply any highlighting on. Here we have to find the component element 
reference from the section. Therefore the double looping 
'getElementComponent' method.

Also when an elements is selected it briefly gets z-index 100 so it is 
moved to the front and visible and manipulatable.

For all elements using radio buttons.

The value may have been null in past versions.

- Now always starts with at least an empty list.
- Compatibility handling no longer sets invalid values. This was only 
temporary anyway but it is better to not do it at all.

Now only sends a list with IDs as value. The actual list manipulation is 
done with Material helper functions (transferArrayItem...).

It is okay to discard a 0 value here, as 0 line height makes no sense 
and it is better to use the default.

Also remove duplicate CSS declaration.

Image are supposed to scale down when needed. This is done via 
max-width.
Small image shall not scale up, which is done with 
object-fit=scale-down.

Delete and duplicate buttons are no longer part of the tab view but are 
always visible below it.

The given serialized properties may not conform to all UIElement 
properties. They are merely meant as a building plan; they may also 
contain outdated properties which have to be transformed when reading.

Basically a div with border properties as usual.

Create object list, when none is existent yet. Otherwise append as 
before.

Now correctly reads the value IDs of drop list elements, so they can not 
be used again.

After a unit definition is read, the deprecated properties are deleted.

This controls the general font size. Specific spans can still be styled 
individually in the text editor.
- The TextEditor also uses this font size as default when rendering the 
text.

see Verona Api