A wing cutout is defined using any combination of eta-xsi-spar-rib-uids. It has the similar syntax to a wingCell.

The cell leading and trailing edge (= forward and rear border) can either be defined by referencing to a spar (->sparUID) or by the defining the xsi (=relative chord) coordinates of the border (xsi1 = inner end; xsi2 = outer end).

The cell inner and outer border can either be defined by referencing to a rib (->ribDefinitionUID and ribNumber) or by the defining the eta (=relative spanwise) coordinates of the border (eta1 = forward end; eta2 = rear end).

Some examples for wing cells can be found in the picture below:

Reference