Shows the position number of a reinforcing bar as defined by XS_REBAR_POSITION_NUMBER_FORMAT_STRING.
For reinforcing bars in tapered bar groups in rebar sets, the
REBAR_POS format is defined by
XS_REBARSET_TAPERED_REBAR_POSITION_NUMBER_FORMAT_STRING, and if that is not set, then by
XS_REBAR_POSITION_NUMBER_FORMAT_STRING.