Resolve "Be compliant with regex used by npm official registry"

doc/user/packages/npm_registry/index.md

@@ -42,6 +42,20 @@ it is not possible due to a naming collision. For example:
 | `gitlab-org/gitlab`    | `@gitlab-org/gitlab`    | Yes       |
 | `gitlab-org/gitlab`    | `@foo/bar`              | No        |
 
+The regex that is used for naming is validating all package names from all package managers:
+
+```
+/\A\@?(([\w\-\.\+]*)\/)*([\w\-\.]+)@?(([\w\-\.\+]*)\/)*([\w\-\.]*)\z/
+```
+
+It allows for capital letters, while NPM does not, and allows for almost all of the
+characters NPM allows with a few exceptions (`~` is not allowed).
+
+NOTE: **Note:** Capital letters are needed because the scope is required to be
+identical to the top level namespace of the project. So, for example, if your
+project path is `My-Group/project-foo`, your package must be named `@My-Group/any-package-name`.
+`@my-group/any-package-name` will not work.
+
 CAUTION: **When updating the path of a user/group or transferring a (sub)group/project:**
 If you update the root namespace of a project with NPM packages, your changes will be rejected. To be allowed to do that, make sure to remove any NPM package first. Don't forget to update your `.npmrc` files to follow the above naming convention and run `npm publish` if necessary.