Add case function documentation (#58868)

Co-authored-by: mc <42146119+mchammer01@users.noreply.github.com>

Author: AllanGuigou

content/actions/reference/workflows-and-actions/expressions.md

@@ -81,21 +81,6 @@ env:
 * {% data variables.product.prodname_dotcom %} ignores case when comparing strings.
 * Objects and arrays are only considered equal when they are the same instance.
 
-{% data variables.product.prodname_dotcom %} provides a way to create conditional logic in expressions using binary logical operators (`&&` and `||`). This pattern can be used to achieve similar functionality to the ternary operator (`?:`) found in many programming languages, while actually using only binary operators.
-
-### Example
-
-{% raw %}
-
-```yaml
-env:
-  MY_ENV_VAR: ${{ github.ref == 'refs/heads/main' && 'value_for_main_branch' || 'value_for_other_branches' }}
-```
-
-{% endraw %}
-
-In this example, we're using a combination of `&&` and `||` operators to set the value of the `MY_ENV_VAR` environment variable based on whether the {% data variables.product.prodname_dotcom %} reference is set to `refs/heads/main` or not. If it is, the variable is set to `value_for_main_branch`. Otherwise, it is set to `value_for_other_branches`. It is important to note that the first value after the `&&` must be truthy. Otherwise, the value after the `||` will always be returned.
-
 ## Functions
 
 {% data variables.product.prodname_dotcom %} offers a set of built-in functions that you can use in expressions. Some functions cast values to a string to perform comparisons. {% data variables.product.prodname_dotcom %} casts data types to a string using these conversions:
@@ -287,6 +272,43 @@ Creates a hash for all `.rb` files in the `lib` directory at root level, includi
 
 `hashFiles('/lib/**/*.rb', '!/lib/foo/*.rb')`
 
+### case
+
+`case( pred1, val1, pred2, val2, ..., default )`
+
+Evaluates predicates in order and returns the value corresponding to the first predicate that evaluates to `true`. If no predicate matches, it returns the last argument as the default value.
+
+#### Example with a single predicate
+
+{% raw %}
+
+```yaml
+env:
+  MY_ENV_VAR: ${{ case(github.ref == 'refs/heads/main', 'production', 'development') }}
+```
+
+{% endraw %}
+
+Sets `MY_ENV_VAR` to `production` when the ref is `refs/heads/main`, otherwise sets it to `development`.
+
+#### Example with multiple predicates
+
+{% raw %}
+
+```yaml
+env:
+  MY_ENV_VAR: ${{ case(
+    github.ref == 'refs/heads/main', 'production',
+    github.ref == 'refs/heads/staging', 'staging',
+    startsWith(github.ref, 'refs/heads/feature/'), 'development',
+    'unknown'
+  ) }}
+```
+
+{% endraw %}
+
+Sets `MY_ENV_VAR` based on the branch: `production` for `main`, `staging` for `staging`, `development` for branches starting with `feature/`, or `unknown` for all other branches.
+
 ## Status check functions
 
 You can use the following status check functions as expressions in `if` conditionals. A default status check of `success()` is applied unless you include one of these functions. For more information about `if` conditionals, see [AUTOTITLE](/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idif) and [AUTOTITLE](/actions/creating-actions/metadata-syntax-for-github-actions#runsstepsif).