Clarify how to use a negated expression in an if statement (#28800)

Co-authored-by: Siara <[email protected]>

Author: albbus-stack

content/actions/learn-github-actions/expressions.md

@@ -23,17 +23,13 @@ Expressions are commonly used with the conditional `if` keyword in a workflow fi
 `${{ <expression> }}`
 {% endraw %}
 
-{% data reusables.actions.expression-syntax-if %} For more information about `if` conditionals, see "[AUTOTITLE](/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idif)."
+{% note %}
 
-{% data reusables.actions.context-injection-warning %}
+**Note**: The exception to this rule is when you are using expressions in an `if` clause, where, optionally, you can usually omit {% raw %}`${{`{% endraw %} and {% raw %}`}}`{% endraw %}. For more information about `if` conditionals, see "[AUTOTITLE](/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idif)."
 
-### Example expression in an `if` conditional
+{% endnote %}
 
-```yaml
-steps:
-  - uses: actions/hello-world-javascript-action@e76147da8e5c81eaf017dede5645551d4b94427b
-    if: <expression> 
-```
+{% data reusables.actions.context-injection-warning %}
 
 ### Example setting an environment variable
 

data/reusables/actions/expression-syntax-if.md

@@ -1,5 +1,11 @@
-When you use expressions in an `if` conditional, you may omit the {% raw %}`${{ }}`{% endraw %} expression syntax because {% data variables.product.prodname_actions %} automatically evaluates the `if` conditional as an expression. However, this rule does not apply everywhere.
+When you use expressions in an `if` conditional, you can, optionally, omit the {% raw %}`${{ }}`{% endraw %} expression syntax because {% data variables.product.prodname_actions %} automatically evaluates the `if` conditional as an expression. However, this exception does not apply everywhere.
 
-You must use the {% raw %}`${{ }}`{% endraw %} expression syntax or escape with `''`, `""`,  or `()` when the expression starts with `!`, since `!` is reserved notation in YAML format.
+You must always use the {% raw %}`${{ }}`{% endraw %} expression syntax or escape with `''`, `""`,  or `()` when the expression starts with `!`, since `!` is reserved notation in YAML format. For example:
 
-Using the {% raw %}`${{ }}`{% endraw %} expression syntax turns the contents into a string, and strings are truthy. For example, `if: true && {% raw %}${{ false }}{% endraw %}` will evaluate to `true`.
+{% raw %}
+
+```yaml
+if: ${{ ! startsWith(github.ref, 'refs/tags/') }}
+```
+
+{% endraw %}