ePiX does not have a separate data structure for lines, but it does provide a function, Line, that draws the line joining a pair of points. Naturally, only a segment can be drawn. ePiX always crops a Line, and in addition removes the half-line that lies behind the observer. Thus, a Line appears as a printed segment, either with ends on the bounding box, or with at most one end in the interior, representing a point on a visible horizon. The Next Generation (a.k.a. ePiX3d or ``Version 2.x'') will supply a line data structure.
A plane is specified by a point and a unit normal vector, or by three non-collinear points. The draw() function renders the lines of intersection of the plane with the faces of the clip box. Unless the clip box has been set manually, these lines of intersection will almost surely avoid the bounding box, and therefore be invisible.