bug#21995: Documentation omission for regular expressions

[jan]

Hi,
\& used as a replacement will substitute in the entire matched
pattern.  For example, given text

hello

and search regexp  \(.\)  with replacement  \&\&  you get

hheelloo

I have not been able to find this \& option in the regular expression
part of the emacs manual.

jan

(Emacs 24.5.1 running on Windows 2008 R2)