Document by using a function
Document by using a function

https://github.com/radiasoft/sirepo/pull/3557#discussion_r624124487
https://github.com/radiasoft/sirepo/pull/3557#discussion_r624124063

mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo