The clip command controls clipping planes. Up to four planes can be active:
Capping of clipped surfaces can be controlled with a preference setting and/or the surface cap command. See also: view, cofr, mousemode
Each plane can be activated or turned off individually; specifying an offset activates a plane if it was not already active. Offsets are in physical distance units (generally Å), with positive values increasing away from the viewer for the near/far planes. The offsets are relative to the position reference point, if given. Otherwise, offsets are relative to the current positions of the planes, or (if a plane is newly activated) the center of the bounding box of displayed models. The position of a plane is forgotten when it is turned off.
The position reference point can be given as x,y,z (three values separated by commas only), an atom-spec, or any of the other standard point specifications.
The axis option sets initial front/back plane orientation as perpendicular to x, y, z, or any of the other standard vector specifications. The default orientation is perpendicular to the line of sight (screen Z).
The screen coordinate system (X horizontal, Y vertical, Z in/out of screen) will be used to interpret position and axis coordinates unless a reference model is specified with the coordinateSystem option.