[boost] regex format string ambiguity

From: John Harris (TT) (john.harris_at_[hidden])
Date: 2002-09-12 13:09:15

in boost regex in 1.27.0, I use the format string, $11$2 to mean "$1, then
'1', then '$2', but it seems as thought regex_merge() is interpreting it as
"$11, then $2".  How can I disambiguate?

jh