MusicXML - how to specify that barline in multi-staff part belongs only to one staff?

Hope this is a suitable place to ask, just trying to figure out from the MusicXML spec how to specify that a barline in a multi-staff part should only be shown on an individual staff, rather than spanning across all staves in the part. Have tried setting the staff number but at least with the few tools I tested, it failed to have the desired effect. The spec doesn't really make it clear if "staff" is a valid property of a barline, but there doesn't seem to be any other way to specify this?
Thanks
Dylan