The kOfxImageEffectPropSetableFielding host property indicates if a plugin is able to change the fielding of the output clip from the default.

The default value of the output clip's fielding is host dependant, but in general,

If the host allows a plugin to specify the fielding of the output clip, then a plugin may do so during the kOfxImageEffectActionGetClipPreferences by setting the property kOfxImageClipPropFieldOrder in the out args argumment of the action. For example a defielding plugin will want to indicate that the output is frame based rather than fielded.