Should spell out prevention for case-insensitive collisions

[yarikoptic]

problem in detail.

the encounter life cycle:

• git on Mac and Windows would complain that file system is case insensitive while cloning a repository where there are files which would collide if case is dropped : truncating git warning datalad/datalad#5925
• while proposing a solution [DATALAD RUNCMD] Move all files from lower cased sub dir into upper case PennLINC/HBN_BIDS#1 , a valid question was asked by @mattcieslak - "how did this pass the validator?"

and well -- upon my search in bids-specification or bids-validator I found no relevant hits. It seems that BIDS nohow instructs to avoid such collisions -- in https://bids-specification.readthedocs.io/en/stable/02-common-principles.html we just say " - an alphanumeric value, possibly prefixed with arbitrary number of 0s for consistent indentation, for example, it is rest in task-rest following task- specification."

I think we should

• extend label description that the value MUST be unique and present in a single casing (e.g. there should also be no sub-S1 and sub-s1 in the same dataset ).
• bids-validator should verify that there is no such collisions (e.g. crude test is len(set(paths)) == len(set([p.lower() for p in paths]))) and issue ERROR

[sappelhoff]

Thanks for bringing this up, I wonder why we didn't run into problems with this much sooner. My gut feeling tells me that your proposed (breaking) change is good and should go into BIDS 1.x as a "bugfix".