You can join two power surfaces together to produce a single continuous surface. It is necessary for the surfaces to both be open or closed in the direction perpendicular to the connection. Additionally, the curves along the joining edges of the surfaces must have the same number of spans.
For example:
The selected curve of the primary surface connects to the closest matching edge curve of the secondary surface, by adding a row of patches between the two surfaces:
Alternatively, click a different secondary surface to undo the append, and create a new appended surface using the new selection.
If the automatically selected edge curve is not correct, select a new edge curve.
The first surface becomes the appended surface and the second surface is deleted. Spines and trim boundaries (and their pcurves) on either surface are deleted.