"definition" element enumeration

[prjemian]

In https://github.com/nexusformat/definitions/blob/main/applications/NXspe.nxdl.xml, the definition field enumerates more than one valid representation of this application definition.

The XML Schema should control how many enumeration item field are allowed for the definition element. In our case, only one value is allowed, not zero (for an application definition), not more than one. The validation process can then properly deliver a message when a data file does not present this structure.

[prjemian]

Additionally, we could allow any case presentation or the NXDL class name to pass validation. Those names that do not match exactly should be flagged as a warning but not marked as invalid.

The NIAC must ensure we do not allow multiple different NXDL classes that have the same name, differing only in case.

[prjemian]

We should fix this situation in NXspe (in #911) by removing line 39:

definitions/applications/NXspe.nxdl.xml

Line 39 in a232ead

<item value="NXSPE"/>

Make a new issue, PR, contact the community, and get approval from the NIAC.

[prjemian]

The manual must make clear how to properly construct an NXDL file that connects this same name with the definition@name=".." attribute in the top-most element and the required enumeration element in the definition field below. This same name (and spelling, and upper/lower case representation) should match the file name. Consider putting this into the manual as a sidebar.

And, any content referenced by the NXDL (such as images) be placed in a subdirectory with the name chosen by stripping off the NX. (as in: NXDL for NXthing would be in file NXthing.nxdl.xml)

file: NXthing.nxdl.xml
resources: thing/image1.png

In the NXDL file:

<definition name="NXthing" ... />

<!-- later -->

        <field name="definition">
            <doc>Official NeXus NXDL schema to which this file conforms.</doc>
            <enumeration>
                <item value="NXthing"/>                
            </enumeration>
        </field>