Be more precise when expression syntax ${{ }} can be omitted in if statement

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

@@ -97,7 +97,6 @@ env:
  **Notes:**
  - {% data variables.product.company_short %} ignores case when comparing strings.
  - `steps.<step_id>.outputs.<output_name>` evaluates as a string. {% data reusables.actions.expressions-syntax-evaluation %} For more information, see "[AUTOTITLE](/actions/learn-github-actions/contexts#steps-context)."
- - {% data reusables.actions.expression-syntax-if %} For more information about `if` conditionals, see "[AUTOTITLE](/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idif)."
  - For numerical comparison, the `fromJSON()` function can be used to convert a string to a number. For more information on the `fromJSON()` function, see "[fromJSON](#fromjson)."
 
  {% endnote %}

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

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