asymptote: GUI usage

 
 11.2 GUI usage
 ==============
 
 A wheel mouse is convenient for raising and lowering objects within
 'xasy', to expose the object to be moved.  If a wheel mouse is not
 available, mouse 'Button-2' can be used to repeatedly lower an object
 instead.  When run from the command line, 'xasy' accepts a command line
 option '-x n', which sets the initial magnification to 'n'.
 
    Deconstruction of compound objects (such as arrows) can be prevented
 by enclosing them within the commands
 void begingroup(picture pic=currentpicture);
 void endgroup(picture pic=currentpicture);
    By default, the elements of a picture or frame will be grouped
 together on adding them to a picture.  However, the elements of a frame
 added to another frame are not grouped together by default: their
 elements will be individually deconstructed (Seeadd).