When something in MacOS-land copies something to the pasteboard, X11.app automatically copies that to the X11-land "clipboard" selection, which is good. But when something in X11-land copies something to the X11 clipboard selection, it is not automatically copied to the OSX pasteboard, and that's lame.

When running XEmacs under X11 (local or remote) I find that

(setq interprogram-cut-function 'own-clipboard
      interprogram-paste-function 'get-clipboard-foreign)

I really wish there was some way to make drag-and-drop of selected text work with XEmacs, though. But that doesn't even work in Linux.

Update: No, scratch that, using interprogram-paste-function is useless. It seems that sometimes copying things in OSX programs updates the X11 clipboard, but not always. I can't figure out when it does and when it doesn't.

Update 2: Incidentally, it is not lost on me that the most frustrating parts of my Mac experience involve X11, which I'm only using at because I just can't put down the Emacs crack-pipe, despite it being the source of much suffering.

Update 3: My current guess as to what is going on is that, every time focus moves from an OSX program to an X11 program, the X11 clipboard is overwritten with the OSX pasteboard (regardless of which is newer). Conversely, when focus moves from an X11 program to an OSX program, nothing is changed at all.

Update 4: Why I don't use Carbon Xemacs: select the following u-umlaut character in Safari -- ü -- copy it; then paste it into Carbon Xemacs and watch it crash. (Oddly, it does not crash if you copy it from Firefox instead of Safari!)

Update 5: Andrew sent me a patch that fixes the Carbon XEmacs crash, yay! I assume it'll be on his site soon.