Reproduced the problem as illustrated here:
Fiddling with file extensions allowed to view and edit e.g. Oto.skeleton.xml in SDK:
Still have no idea how to reverse this.
It is for educational purposes, and the ultimate goal is to manipulate 2D images to create a 3D model purely by coding (e.g. using Java and XML in this case), rather than by using a 3D creation suite like Blender where you mostly just click, select, drag and drop etc. (similar to Scene Builder for JavaFX apps).
It is for a computer science final year project, so I have to make sure the focus is mainly on the coding (of course I could cheat by using Blender and simply making sure I understand every line of code in the generated xml document, shh) to differentiate it from e.g. an art final year project.
I understand you saying it doesn’t make sense here, because of course in real life efficiency is respected more than “unnecessary” studying to simply understand how something works, rather than using that thing to achieve what you want if it works without worrying about who made it or how it was made. I agree, trying to make something like a .blend from scratch purely by writing code lines cannot make any sense outside of school.
If someone fiddles with the extensions and figures how to get the SDK to re-recognise .mesh.xml as an OgreXML please let us know.