Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/system/templates/menu-local-tasks.html.twig

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+{#
+/**
+ * @file
+ * Default theme implementation to display primary and secondary local tasks.
+ *
+ * Available variables:
+ * - primary: HTML list items representing primary tasks.
+ * - secondary: HTML list items representing primary tasks.
+ *
+ * Each item in these variables (primary and secondary) can be individually
+ * themed in menu-local-task.html.twig.
+ *
+ * @see template_preprocess_menu_local_tasks()
+ *
+ * @ingroup themeable
+ */
+#}
+{% if primary %}
+  <h2 class="visually-hidden">{{ 'Primary tabs'|t }}</h2>
+  <ul>{{ primary }}</ul>
+{% endif %}
+{% if secondary %}
+  <h2 class="visually-hidden">{{ 'Secondary tabs'|t }}</h2>
+  <ul>{{ secondary }}</ul>
+{% endif %}