For local data suppliers we needed to exclude
: from being used as separators for data suppliers as from finder you couldn’t give a file or folder a name with a
: and from the terminal it is difficult to include a
/ in a file or folder name.
_ became the separator for local data suppliers. And for data supplier plugins.
It's not used for local data suppliers anymore but the convention stayed.
/ convention for symbols is going away anyway, more on that soon)