Global vs file-level _parameters

[SharkWipf]

Currently, an optional _parameters field is allowed both on the root level and on each data_entry level (i.e. per-file).
Thus allowing both per-file and global parameters.
The flexibility is nice, but it might be confusing.

Are there any use cases in which parameters are necessary on a global level?
I could imagine that a complex format consisting of many different files could want to store information about what file contains what and how many files there are in total, beyond the capabilities of the data_entry key system.
But this is a hypothetical scenario that kinda stretches the imagination.

Can anyone come up with anything more concrete, more to the point, for why global _parameters could be necessary?
Alternatively, would it be better to keep it "just in case", or should we remove it?

[simonbethke]

Those are different purposes. You need per file if you want to add data per file. And obviously global for data that doesn't belong to a file.
In general "parameters" is just a giant write-only read-never trashbin. The actual parameters should be listed here

[simonbethke]

For displaying not. But for using yes (for specific cases)

[simonbethke]

a transform-matrix is also not required for viewing an object. But if you don't have it, you display it in the wrong position

[SharkWipf]

Then that (focal-length) would fall under _meta still. Information that can be useful but is not required to open/view the file/scene.

[simonbethke]

But it cannot be useful if it has not been defined/normalized.

[SharkWipf]

As long as a generating and an opening application both decide on the same naming convention, that's good enough. Others will sooner or later follow the same convention.
That said, as mentioned elsewhere, I'm not against pre-defining what we can and having other, non-standardized keys require a prefix.