It's used at build time in 6 crates.

Depender (with downloads and own rev deps) quickfix-msg-gen version
340 quickfix-msg43 build ^0.1.0
330 quickfix-msg40 build ^0.1.0
320 quickfix-msg42 build ^0.1.0
320 quickfix-msg41 build ^0.1.0
270 quickfix-msg50 build ^0.1.0
120 quickfix-msg44 build ^0.1.0