Merge branch 'docupdate' into 'main'

Add to trouble shooting

See merge request GeoModelDev/GeoModel!310

documentation/docs/components/geomodelxml/troubleshooting.md

@@ -2,6 +2,20 @@
 
 Some typical errors that can happen, and how to debug and/or solve them. This is an evolving list and may differ depending on the specific version of `GeoModelXML`, as bugs are solved and others revealed.
 
-- `evaluate: invalid expression. Last good expression was ...`:
+- **`evaluate: invalid expression. Last good expression was ...`**:
 
     This error indicates an issue when XML is being parsed. Check for typos or invalid syntax in defining parameters, providing names to `logvolref`, etc.
+
+- **`WARNING: No valid FullPhysicalVolume found` or `WARNING: no GeoAlignableTransform found!`**:
+
+   This error can occur when `alignable` properties are not correctly set by all elements consistently. Normally this needs to be set in three places, 
+    - a) a `multicopy` or `transform` which should set `alignable="n"` where `n` is the "level" at which it is alignable (scheme defined by the client code, not `GeoModelXML`, so the user can choose any value they deem appropriate).
+    - b) a `transformation` applied within the `multicopy`/`transform` should set `alignable="true"` so that a `GeoAlignableTransform` will be created for this transformation, allowing alignment corrections to be applied.
+    - c) the `logvol` or `assembly` to which the above `multicopy`/`transform` and `transformation` are being applied should set `alignable="true"` when it is created, so that a `GeoFullPhysVol` will be created, which can be associated with alignment corrections. 
+
+- **`unable to open external entity ...`**: 
+   
+   This error can happen when a tool cannot properly resolve relative paths to entities within an XML file. Generating a single file from the separate files as follows can help make a geometry more "portable":
+   ```
+   xmllint --noent --valid PATH/TO/FILES/MySplitUpGeometry.gmx > MyCombinedGeometry.xml
+   ```