I wonder how to use the wml2:verticalDatum-element. We have a measurement timeseries of water height in a river with values relative to a certain height. This height is given relative to a verticalDatum , EPSG 5783 in our case. Strictly speaking I think that I would have to create a "new" verticalDatum, the translated EPSG 5783 and store it in the wml2:verticalDatum-element. But this seems useless because everybody knows EPSG 5783 and translation operation but nobody knows "my" verticalDatum.
Thus my proposition is to store the information in the gml:identifier-subelement as shown in attached image "getFOI-response_identifier", there the "certain height" is 37.5 m.
The anchorDefinition-element, as used in attached image "MonitoringPoint", is not meant to store this in my opinion, as it is meant to store the "origin" or "fundamental point" in a geodetic sense , which is something different.