As a mod author, how am I intended to use this? The player could have any number (or none!) of other bz mods installed. Is the idea to list this as the dependency then check for the other mods directly after?

This is purely to enforce mod load order. Basically, if you have a mod that should load after all other mods (eg. DSR/Deadlock Stacked Recipes) then you can add this as an optional dependency, and then if the player uses any BZ mods (even future ones), the mod load order will be enforced, and you won't need to keep updating your dependencies every time i release a new mod.

Thanks!

Hmmm this only works if bz-dsr-bridge is actually loaded though, and if someone is just using a few BZ mods, they probably won't have installed it...