Automatic pager invocation

There's a missing middle ground between a full tty (where you can use cursor movement commands) and sending output to a file. Another example is Emacs's shell-mode. If it didn't return true to isatty() then gzip might write binary data to stdout, and other programs wouldn't prompt interactively. So it has to claim to be a tty, but then some tools want to run a pager or do cursor movement.

There should be a similar function isinteractive() provided by the C library and kernel somehow. When you create a pty you can specify whether it should be a full terminal (returning true to both isatty() and isinteractive()) or just a kind of interactive thingy (isinteractive=true but isatty=false). I guess if any computer museums are using real printing terminals they could also benefit from this. You don't want to run less(1) on your Teletype, though I guess more(1) could work.