"Unknown" modalities are mentioned in the text

[yarikoptic]

ran into while reviewing #475 . Text refers to RARE and FLASHsubsampled although none such is listed among known modalities

$> git grep -e RARE  -e FLASHsubsampled                                    
src/04-modality-specific-files/01-magnetic-resonance-imaging-data.md:are used to record the same modality (e.g. RARE and FLASH for T1w) this field
src/04-modality-specific-files/01-magnetic-resonance-imaging-data.md:distinction (e.g. just between RARE and FLASH, or between RARE, FLASH, and
src/04-modality-specific-files/01-magnetic-resonance-imaging-data.md:FLASHsubsampled) remains at the discretion of the researcher.

[effigies]

These appear to be suggestions for acq- values.

bids-specification/src/04-modality-specific-files/01-magnetic-resonance-imaging-data.md

Lines 156 to 169 in abf6f73

	#### The `acq` entity
	The OPTIONAL `acq-<label>` key/value pair corresponds to a custom label the user
	MAY use to distinguish a different set of parameters used for acquiring the same
	modality. For example this should be used when a study includes two T1w images -
	one full brain low resolution and and one restricted field of view but high
	resolution. In such case two files could have the following names:
	`sub-01_acq-highres_T1w.nii.gz` and `sub-01_acq-lowres_T1w.nii.gz`, however the
	user is free to choose any other label than `highres` and `lowres` as long as
	they are consistent across subjects and sessions. In case different sequences
	are used to record the same modality (e.g. RARE and FLASH for T1w) this field
	can also be used to make that distinction. At what level of detail to make the
	distinction (e.g. just between RARE and FLASH, or between RARE, FLASH, and
	FLASHsubsampled) remains at the discretion of the researcher.

Edit: I guess that's obvious, but I'm not sure there's an implication that these correspond to modalities as well as just sequence names, if that's what's you're supposing.

[yarikoptic]

nah, I think I just rushed into filing an issue... indeed it makes sense to annotate "peculiar" acquisitions for which we have no suffix in acq-.