An <map-input type="zoom" ...> is required for <map-link rel="tile" ...> even though it may not be necessary

[prushforth]

The fact that the zoom input is necessary in this case is a bug:

<map-extent units="CBMTILE">
  <!-- this is necessary, but that's a bug, I think -->
  <map-input name="z" type="zoom" value="25" min="0" max="25"></map-input>
  <map-input name="txmin" type="location" rel="tile" position="top-left" axis="easting" units="tilematrix" ></map-input>
  <map-input name="tymin" type="location" rel="tile" position="bottom-left" axis="northing" units="tilematrix" ></map-input>
  <map-input name="txmax" type="location" rel="tile" position="top-right" axis="easting" units="tilematrix" ></map-input>
  <map-input name="tymax" type="location" rel="tile" position="top-left" axis="northing" units="tilematrix" ></map-input>
  <map-link rel="tile" tref="https://datacube.services.geo.ca/ows/msi?SERVICE=WMS&REQUEST=GetMap&FORMAT=image/png&TRANSPARENT=TRUE&STYLES=msi-color&VERSION=1.3.0&LAYERS=msi&WIDTH=256&HEIGHT=256&CRS=EPSG:3978&BBOX={txmin},{tymin},{txmax},{tymax}" ></map-link>
</map-extent>

The fact that there is a <map-link rel="tile"...> should be enough to go by.

If the <map-input name="z" type="zoom" value="25" min="0" max="25"></map-input> is not present:

<map-extent units="CBMTILE">
  <map-input name="txmin" type="location" rel="tile" position="top-left" axis="easting" units="tilematrix" ></map-input>
  <map-input name="tymin" type="location" rel="tile" position="bottom-left" axis="northing" units="tilematrix" ></map-input>
  <map-input name="txmax" type="location" rel="tile" position="top-right" axis="easting" units="tilematrix" ></map-input>
  <map-input name="tymax" type="location" rel="tile" position="top-left" axis="northing" units="tilematrix" ></map-input>
  <map-link rel="tile" tref="https://datacube.services.geo.ca/ows/msi?SERVICE=WMS&REQUEST=GetMap&FORMAT=image/png&TRANSPARENT=TRUE&STYLES=msi-color&VERSION=1.3.0&LAYERS=msi&WIDTH=256&HEIGHT=256&CRS=EPSG:3978&BBOX={txmin},{tymin},{txmax},{tymax}" ></map-link>
</map-extent>