While reading the common derivatives draft as the rendered version of #265, I noticed that for SpatialReference it uses an absolute path:

    "SpatialReference": "/sub-01/anat/sub-01_desc-combined_T1w.nii.gz"

whereas in the existing MRI examples there is

   "IntendedFor": "func/sub-01_task-motor_bold.nii.gz"

and in the EEG examples there is again

  "IntendedFor":"/sub-01/ses-01/anat/sub-01_T1w.nii",

This made me realize that the specification is not clear w.r.t. references to other files. E.g. in the SpatialReference case (which is in the derivative folder): would that point to a file in the derivative itself, or could it also point to a file at a higher level (e.g. the raw level)? In this case I know it points within the derivative dataset since it contains the desc keyword (which is not defined for raw). But had it been /sub-01/anat/sub-01_T1w.nii.gz, then I would have said that it must have been pointing to a file in the raw dataset. The specification of a relative path, and the specification of what specifically it is relative to, might avoid confusion.