TODO

Add elements (with or without parents)
Non-recursive delete (move up children elements)

Select:
    - leafs (orphant elements)
    - Direct children

Get properties:
    - if an element has a parent
    - if an element has children
    - level in the tree of the element !!!

Get a path for current element (navigation path)

Handle getParent with a detph value (default is first)

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-- Unit tests --
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- Assert return values are what they should be (arrays mostly)

- Assert that there's no "hole" when deleting/moving/adding elements
- Assert there's no cross ids when deleting/mobing/adding elements

- Assert XML output is valid
- Assert Array output is an array