Re: should query-replace-regexp-eval be in the manual?

[Richard Stallman]

    Basically it has been my experience that query-replace-regexp-eval is
    a nice idea, but in practice quite unusable.  \, achieves a similar
    purpose but with a much more convenient interface.

Could you write some text to document the \ feature in the Emacs Manual?

    To get back to the original question: since \, has all of the
    functionality of query-replace-regexp-eval with a more convenient
    interface, query-replace-regexp-eval could be considered obsolete or
    at least obscure.

I think its doc string should mention that the \ feature is more
convenient for interactive use, and the function should be marked
obsolete.