This seems like a simple question, but the docs don't seem to have anything to say on the subject. I would like to do something like Requires: vim or emacs but when I do that, I in fact depend on vim, or and emacs. What is the syntax for depending on one or another of two packages?
The standard way to do this is via virtual provides: the providing RPMs each state that they provide a virtual package, and the dependent RPM requires that virtual package. So, in your example, vim and emacs both Provides: text-editor, and your package would Requires: text-editor.
If the packages that you're depending on don't provide an appropriate virtual package, you could probably hack around this by making up your own. Make dummy my-package-vim-mode and my-package-emacs-mode RPMs that Requires: vim and Requires: emacs, respectively, and Provides: my-package-text-editor, then have your package Requires: my-package-text-editor.