What problem does this feature solve?

I don't seem to be able to find any documentation on how to handle custom directives in a vue/vue.config.js/webpack setup using latest 3.1.* Vue. I have resorted to not using directives, but these would be a handy tool in our toolbox.

Does anyone know how to achieve this, or where I could find documentation on the matter?

What does the proposed API look like?

Can you open an issue on the vuejs/docs repo please?