Get all items / elements of the actual unit to validate.
Loop the units and validate each item in unit.
Apply the rules specified in setting to the item.
Take care of candidates already validated and the items already added to this_unit.
Todo
check context of replacement: do not add links in links, or inline of overlapping elements, ... replace only one item of an entity > e.g. A. Merkel, Mum Merkel, ...