15.3.21 Boost Format Strings

Boost format strings are described in the documentation of the boost::format class, at https://www.boost.org/libs/format/doc/format.html. In summary, a directive has either the same syntax as in a C format string, such as ‘%1$+5d’, or may be surrounded by vertical bars, such as ‘%|1$+5d|’ or ‘%|1$+5|’, or consists of just an argument number between percent signs, such as ‘%1%’.