better naming of page fitting

envelope.asy

@@ -1,9 +1,12 @@
 from settings access outformat;
 outformat="pdf";
 unitsize(1mm);
+
+//A4: 210 x 297 mm
 int pgw = 210;
 int pgh = 297;
 size(pgw, pgh);
+bool force_output_size = true;
 
 int sqsz = pgw;
 
@@ -15,12 +18,12 @@ string envfmt = "C6";
 
 // debugging tool
 bool with_labels = true;
-bool force_a4 = true;
 
 
 // It is unpractical to try emulating second quadrant. We will work in the
 // first quadrant with the origin at the bottom-left corner of the square (not
 // the whole page). Therefore, the bottom edge of the page is at y=(210-297)
+// for an A4 paper
 int pgbot = pgw - pgh;
 
 // gimme a square?
@@ -115,9 +118,9 @@ draw(cl1 -- (0, sqsz) -- ct2);
 draw(ct1 -- cr1);
 draw(cr2 -- (sqsz, 0) -- cb1);
 
-//Force A4 output size
-path a4_outline = (0,pgbot) -- (0, sqsz) -- (sqsz, sqsz) -- (sqsz, pgbot) -- cycle;
-if (force_a4) {
-	draw(a4_outline, invisible);
-	clip(a4_outline);
+//Force declared output size
+path output_outline = (0,pgbot) -- (0, sqsz) -- (sqsz, sqsz) -- (sqsz, pgbot) -- cycle;
+if (force_output_size) {
+	draw(output_outline, invisible);
+	clip(output_outline);
 }