Emacs technique for comparing sections of documents?

I'd like to be able to open two windows in Emacs, select a region of text in each window, and get a comparison of the difference between the two selections.

This would be very handy for a large-scale maintenance project, where I'm working on a version tree with multiple branches, lots of copy/paste, and code that is being moved around sporadically.

I've found a paid-for tool that does provide this function (Ultracompare), but it's windows-speci开发者_运维技巧fic, and I need a solution that runs on Solaris/Linux.

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I think M-x ediff-regions-wordwise does what you want.

Run ediff-regions-wordwise and Emacs will prompt for each buffer, then prompt you to select (or confirm) a region in the buffer.

And, bonus, Emacs runs on Windows too!

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I'd be inclined to use narrow-to-region (C-x n n) in both buffers followed by M-x compare-windows if only because it has worked for me for at least 100 years. :-)