From the angular docs:
Best Practice: In order to avoid collisions with some future standard, it's best to prefix your own directive names. For instance, if you created a <carousel> directive, it would be problematic if HTML7 introduced the same element. A two or three letter prefix (e.g. btfCarousel) works well. Similarly, do not prefix your own directives with ng or they might conflict with directives included in a future version of Angular.
See the Creating Directives section of the Angular Docs.
From the angular docs:
See the Creating Directives section of the Angular Docs.