User talk:2605:A000:D18A:E000:D47C:481:DC6C:9A87

I'm not an editor, but here is a potential citation for the section on "the leg line" as an explanation for the phrase "break a leg" in theater.

Historical Dictionary of American Theater: ModernismBy James Fisher, Felicia Hardison Londré(Page 102, actual section on the topic.) Book is written by 2 authors with significant experience & knowledge of the topic of theater.