As the comment says, this row is needed by the `ieshiv` grunt task because the `<tab-heading>` tag can be used when building a `tabSet` but it does not correspond to an angular directive, instead it is parsed by the `tab` directive as you can see [here](https://github.com/redaemn/bootstrap/blob/7084248b3707fbb52fcf9bcdfd42d1d41b2d19e8/src/tabs/tabs.js#L114). The `ieshiv` task searches the sources to find all directives declarations and without this line it wouldn't find it.

Maybe I should find a cleaner solution, maybe define an empty tabHeading directive... ideas?