Re: display.texi: (<line>,<col>) isn't documented.

[Richard Stallman]

    Yes, but its size is not obvious, especially if part of it is off-screen.

    The size indication can be helpful when coding, to see how long a given
    string of characters is. It can also be useful as a sanity check when you
    use C-w.

When the region is that large, would you really know the right length
well enough to recognize a wrong length?

Can you tell me how, in practice, you recognize from the displayed
length that the region is wrong?