Compositing in 3D Space with Action > About Source Nodes > Replacing the Front or Matte Clip >

Source Settings

Source box: Select a Front or Matte source.

Override button: Enable to override a source node selection on the parent source.

Source Type box

Select a source type. When selecting Custom, you can also designate a Front and Matte type in the boxes below.

Select:	To:
Front only	Set the source to use only the front of the selected surface; the matte will be replaced with white (displayed as FW under the selected surface in the schematic).
Matte only	Set the source to use only the matte of the selected surface; the front will be replaced with white (displayed as WM under the selected surface in the schematic).
Custom	Set the source to have all the options of replacing the front and the matte of the selected surface by White, original Front or original Matte.

Front Type box: Select the clip to use as the front from the image parented by the source.

Matte Type box: Select the clip to use as the matte from the image parented by the source.

Source View box: Select which source to view in the image window. See Viewing a Source Node.