It's used at build time in 6 crates.

Depender (with downloads and own rev deps) quickfix-msg-gen version
260 quickfix-msg44 build ^0.1.0
170 quickfix-msg42 build ^0.1.0
170 quickfix-msg40 build ^0.1.0
170 quickfix-msg43 build ^0.1.0
170 quickfix-msg41 build ^0.1.0
170 quickfix-msg50 build ^0.1.0