JavaScript libraries may use the custom data attributes, as they are considered to be part of the page on which they are used. Authors of libraries that are reused by many authors are encouraged to include their name in the attribute names, to reduce the risk of clashes. Where it makes sense, library authors are also encouraged to make the exact name used in the attribute names customizable, so that libraries whose authors unknowingly picked the same name can be used on the same page, and so that multiple versions of a particular library can be used on the same page even when those versions are not mutually compatible.
This is saying that if you have `data-thing`, then putting your own name in there is better, like `data-mylib-thing` to tell it apart from `data-yourlib-thing`, but the ultimate in flexibility and compatibility is if the end-user of your library can configure this part so they can safely tell `data-yourlib-v3-thing` apart from `data-yourlib-v4-thing` etc.