x1 is arranged and to be traced/read in boustrophedon manner, starting at point x2, turning at points x3 (ordered list), and ending at point x4.
x1 need not be a script (for example: it could just be a winding curve/maze/path/pattern, a snake curled up withoutcoiling on top of itself, or yarn while weaving or on a loom). If not orientation is preferred, then x2 and x4 may be mutually exchangeable if the x3 is reversed. See also: toxsotiseira.