Tim Bunce wrote: > That's going to cause pain when people using older parsers try to read > docs written for newer ones. Would a loud warning plus some best-efforts > fail-safe parsing be possible?
Indeed. And that's a important use-case. But best-effort is difficult when you're talking about future-compatibility of core constructs, which these are supposed to be. I guess best-effort for uppercase (semantic) mark-up is just to map: =begin UNKNOWN mumble mumble mumble =end UNKNOWN to: =head1 UNKNOWN =begin para mumble mumble mumble =end para But it's harder to see how to cope with unknown all-lower directives: =begin frobnication ... =end frobnication =for franistat =wassname Especially the last of those, since it might be either an abbreviated block or a pure directive. I suspect that these should either still be fatal, or they should warn-and-ignore. Damian