Update docs on using concurrency to auto-cancel redundant jobs / runs

data/reusables/actions/actions-group-concurrency.md

@@ -23,3 +23,31 @@ concurrency:
  cancel-in-progress: true
 ```
 {% endraw %}
+
+### Example: Using a fallback value
+
+If you build the group name with a property that is only defined for specific events, you can use a fallback value. For example, `github.head_ref` is only defined on `pull_request` events. If your workflow responds to other events in addition to `pull_request` events, you will need to provide a fallback to avoid a syntax error. The following concurrency group cancels in-progress jobs or runs on `pull_request` events only; if `github.head_ref` is undefined, the concurrency group will fallback to the run ID, which is guaranteed to be both unique and defined for the run.
+
+{% raw %}
+```yaml
+concurrency: 
+ group: ${{ github.head_ref || github.run_id }}
+ cancel-in-progress: true
+```
+{% endraw %}
+
+
+### Example: Only cancel in-progress jobs or runs for the current workflow
+
+ If you have multiple workflows in the same repository, concurrency group names must be unique across workflows to avoid canceling in-progress jobs or runs from other workflows. Otherwise, any previously in-progress or pending job will be canceled, regardless of the workflow.
+
+To only cancel in-progress runs of the same workflow, you can use the `github.workflow` property to build the concurrency group:
+
+{% raw %}
+```yaml
+concurrency: 
+ group: ${{ github.workflow }}-${{ github.ref }}
+ cancel-in-progress: true
+```
+{% endraw %}
+