message-subject-trailing-was-ask-regexp

message-subject-trailing-was-ask-regexp is a variable defined in `message.el'.
Its value is

"[ 	]*\\([[(]+[Ww][Aa][Ss]:?[ 	]*.*[])]+\\)"

Documentation:
*Regexp matching "(was: )" in the subject line.

The function `message-strip-subject-trailing-was' uses this regexp if
`message-subject-trailing-was-query' is set to the symbol `ask'. If
the variable is t instead of `ask', use
`message-subject-trailing-was-regexp' instead.

It is okay to create some false positives here, as the user is asked.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.