Add human statement to emphasize that _desc is the last entity

[yarikoptic]

Partially addresses #1895

attn @arokem

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.23%. Comparing base (77ad779) to head (573a4c6).

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##           master    #1915   +/-   ##
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  Coverage   87.23%   87.23%           
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  Files          16       16           
  Lines        1410     1410           
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  Hits         1230     1230           
  Misses        180      180           

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[arokem]

Thanks! I don't think this quite covers the issue raised in #1895 though, because this points to a specific example, without stating explicitly that this is the convention for other cases as well. Does that make sense?

[yarikoptic]

Good observation @arokem ! our problem is that we do not really introduce _desc anywhere before. For now I just adjusted original description that it doesn't really close that issue, but I think for this could be a quick enhancement.

[effigies]

I realized the other day that I now wish that we had put hemi- last. e.g., this would be preferable:

sub-01_desc-custom_hemi-L_white.surf.gii
sub-01_desc-custom_hemi-R_white.surf.gii
sub-01_desc-freesurfer_hemi-L_white.surf.gii
sub-01_desc-freesurfer_hemi-R_white.surf.gii

to

sub-01_hemi-L_desc-custom_white.surf.gii
sub-01_hemi-L_desc-freesurfer_white.surf.gii
sub-01_hemi-R_desc-custom_white.surf.gii
sub-01_hemi-R_desc-freesurfer_white.surf.gii

It seems to me that desc- is not a grouping entity, like echo- or part- (or hemi-) and generally we probably want grouping entities toward the back and distinguishing entities toward the front.

So if we have something like components and a mixing matrix that are distinguished by entity, we might prefer:

sub-01_task-rest_desc-ICA_<key>-components_<suffix>.<ext>
sub-01_task-rest_desc-ICA_<key>-mixing_<suffix>.<ext>

This is not grounded in a particular BEP, but just a thing to consider before we codify this.

[yarikoptic]

I think your motivation @effigies relates to fresh

• Introducing chaining rule for derivatives #1949

as a more generic rule of entities composition.

generally we probably want grouping entities toward the back and distinguishing entities toward the front.

well, sub- is a very groupping entity ;) overall it all depends on the case and there might be no universally best order. May be could be in part or fully addressed as part of the

• Make it possible to specify folders layout to be other than sub-{label}/[ses-{label}/] bids-2-devel#54
• (some drafty beginning of work on it): https://github.com/bids-standard/bids-specification/pull/1809/files#diff-efe09d8f5bbcea3e5772ac9f06f13e149454fbdfc00b1aa286a25aac7c2d7303R185

as that one already would require change of the order of entities in the folders/filenames. Hence could as well be extended to the customization of entities to fit "the best" order.

[effigies]

To be clear, by "grouping entity", I mean one that can be varied without changing the overall meaning of the files. Different parts or echos indicate multiple files that should be considered together. Different tasks or subs need separate consideration.