x1 is arranged and to be traced/read in the manner of reading modern Latin script for English (from side to side along a line segment, then suddenly jumping back to the original side but on a nonintersecting coparallel line segment and proceeding in the same direction, with gross movement being perpendicular to each of these line segments and in a constant direction), starting at point x2, jumping at points x3 (ordered list of pairs, the first term of which is the end point of one line segment and the second term of which is the starting point of the immediately following line segment), and ending at point x4.
No mention of "left-to-write, top-to-bottom", etc. (although these are examples). See also: bolstropfedo.