<Invalid Parent> (non-repetitive exit [not required]): The parent object,
if it does not contain any child element.
<Invalid Item> (non-repetitive exit [not required]): The item to add,
if the parent does not contain the matching data element to update.
<Invalid Index> (non-repetitive exit [not required]): The value of <Index>,
if it is smaller than 1 or larger than the size of the list plus 1.
If an invalidity is detected, but the relevant exit
(<Invalid Parent>, <Invalid Item> or <Invalid Index>) is missing,
an exception is thrown.
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