When you try to log in to the Wikipedia web site, if you mistype the password or
the user name than the user name and password is written back.
Thought repeating the password field as well makes us one field less when we
don't type our user name correctly, I think it is a big security problem to put
it in the web page. Perhaps not replying would be the best.
Go to the Wikipedia login page Mistype your user name or password (or both) The page saying "login error" comes. Now right click on the page and say
Look for the string "password", and you'll see the types password appears in
the web page.