openproject/frontend/app/templates/work_packages/watcher_button.html

<button class="button"
        ng-click="toggleWatch()"
        title="{{ buttonTitle }}"
        id="{{ buttonId }}">
    <i class="button--icon" ng-class="watchIconClass"></i>
    <span class="button--text"
          ng-if="showText"
          ng-bind="buttonText">
    </span>
</button>