I think preserving unknown MetaData is actually a mistake.


Having extra metadata to use in your local software package is
okay. But the main point of GIFTI is as an exchange format.

Also, having to write a new file B.gii from an existing file A.gii
means having a reason to modify it.

Those 2 points together mean that if the software that wrote file
A.gii gets file B.gii back, they will have no idea what sorts of
changes were done. Therefore, the assumptions it is likely to make
based on the old copied MetaData may be invalid.

For example, suppose Caret creates a dataset that has their own
'orientation' and 'coordframe_id' values set as MetaData. Now AFNI
gets that file and performs some transformations on it, and writes
it back out. Now someone takes it back to Caret.

If AFNI preserves that unknown metadata, it is probably garbage
when it gets back to Caret. From Caret's perspective, who knows
what hideous manipulations were performed in AFNI? At that point,
only agreed upon GIFTI metadata is reliable.

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So anyway, if certain MetaData is essential for not mis-interpreting
the dataset, then we need to use publicly agreed upon ways of passing
it along.

If that MetaData is not essential and is not understood by the
reading software, then it should be thrown out. It can no longer be
relied on to survive whatever computations are being performed.

My $0.02,

- rick