Examples of GML fragment in ISO 19115/19139 gmd:verticalElement

Next one is vertical.

Meteorology is really indifferent about the concept of CRS, so there is
bunch of altitude data without reference system specification. Luckily there
is EPSG:5714 registered as "msl height" so we can express it in globally
understood framework.

<gmd:verticalElement>
<gmd:EX_VerticalExtent id="boundingVerticalExtent">
<gmd:minimumValue>
<gco:Real>7.7</gco:Real>
</gmd:minimumValue>
<gmd:maximumValue>
<gco:Real>7.7</gco:Real>
</gmd:maximumValue>
<gmd:verticalCRS>
<gml:VerticalCRS gml:id="crs.msl_height">
<!-- EPSG:5714 simply means "msl height" -->
<gml:identifier codeSpace="urn:ogc:def:crs:EPSG::">5714</gml:identifier>
<!-- instruction in ISO 19136 12.2.3.4 -->
<gml:scope>not known</gml:scope>
<gml:verticalCS/>
<gml:verticalDatum />
</gml:VerticalCRS>
</gmd:verticalCRS>
</gmd:EX_VerticalExtent>
</gmd:verticalElement>

What if we use pressure coordinate or height above surface? I don't know.
Maybe WMO has to do something. It's just a creating couple of URI and code,
so it should be easy if people understands the way.