It's used at build time in 6 crates.

Depender quickfix-msg-gen version
quickfix-msg44 build ^0.1.0
quickfix-msg41 build ^0.1.0
quickfix-msg42 build ^0.1.0
quickfix-msg50 build ^0.1.0
quickfix-msg43 build ^0.1.0
quickfix-msg40 build ^0.1.0