“mappend” associates additional command line operations with a particular movie frame. These “generalized movie commands” will be executed every time the numbered frame is played.

mappend frame: command

frame = integer: the frame to modify

command = literal command-line text

mappend 1: hide everything; show sticks 
mappend 60: hide sticks; show spheres 
mappend 120: hide spheres; show surface 

The “mset” command must first be used to define the movie before “mdo” statements will have any effect. Redefinition of the movie clears any existing movie commands specified with mdo or mappend.

mset | madd | mdo | mplay | mstop | cmd.mappend | commands