The DataOpen message has a little-supported, never-documented “template mode” used for launching temporary files, help files, template files (not Template files you understand) and so forth – anything that you don’t want written back to where it was loaded from. Acorn supported it from RISC OS 2.00, but only in !Edit and !SrcEdit for some reason and it faded from memory, which is a great loss because it’s rather useful.

DataOpen template mode is selected by setting the unsafe flag to -2. I have supported it on all my editors for years, and I recommend you do too, it’s very simple – if you load a file in a DataOpen and unsafe=-2, reduce your filename to just the leaf... that’s all! I have patched Zap to support it. It’s also the best way of opening help files that you don’t want the user to accidentally change.

This is a file launcher (like a mini-Filer) which allows you to test your DataOpen template mode support. As a bonus, if the DataOpen is ignored (because there’s no suitable program running already) it attempts to launch a suitable editor and tries again. This will not always be successful because Alias$@RunType variables are not necessarily effective without a filename (do try to ensure that yours are though). However, this is just a bit of bonus behaviour (simulating the Filer in effect) – it’s perfectly acceptable to simply open a query window and complain if no suitable editor is running.