Reject non-finite float bounds, unplain integer args, constant samples, a constant zero divisor and the default separator; a binding key is no path segment; ascii keeps DEL; an unheld path panics

path.go

@@ -40,7 +40,7 @@ func walkPath(n node, tail []string, w pathWalk) error {
 				return err
 			}
 		}
-		child, ok := n.fields[tail[0]]
+		child, ok := n.field(tail[0])
 		if !ok {
 			return fmt.Errorf("no field %q", tail[0])
 		}