-A gline duration may be specified in seconds, or in the format
-1y2w3d4h5m6s - meaning one year, two weeks, three days, 4 hours, 5
+A G-line, Z-line or shun duration may be specified in seconds, or in the
+format 1y2w3d4h5m6s - meaning one year, two weeks, three days, 4 hours, 5