They are aliases. Angular allows both in order to name a directive. The data-ng-repeat allows the HTML to be validated through validators that do not understand Angular.
The documentation is here with directives.
This is from the docs:
Angular normalizes an element's tag and attribute name to determine
which elements match which directives. We typically refer to
directives by their case-sensitive camelCase normalized name (e.g.
ngModel). However, since HTML is case-insensitive, we refer to
directives in the DOM by lower-case forms, typically using
dash-delimited attributes on DOM elements (e.g. ng-model).
And all these are valid:
AFAIK, you can use these naming conventions in any directive that Angular parses.
