RE: faq.texi

[Drew Adams]

    >Maybe I'm weird, but I do tend to use C-y reasonably often in a
    >specific circumstance:  when i want to see how well two regions of
    >text match, I go to the beginning of one, and hit C-y until the search
    >fails; this could be done with C-w too but it's a lot more tedious for
    >big regions.

    I do this, too - more precisely, C-y through
    one region until the regexp highlighting stops on the other.

Is this mostly (only?) useful for different areas of the same buffer (since
you mention isearch highlighting other areas)? I assume you didn't literally
mean "region" here, but just "section" of text, no?

For comparing text sections in two different buffers, I usually select them,
`C-x n n', and use ediff on them. For sections in the same buffer, I
sometimes paste one section into a new buffer and do the same.

Maybe your technique would be handier (quicker) in that case, at least to
find a first difference. But IIUC, the two sections would need to be visible
simultaneously - e.g. near each other or in different windows.