docs(custom-placeholders): add expressions deconstructions, update headings (#506)

Author: rohalskyy

src/content/docs/enterprise/organization-management/settings/custom-placeholders.mdx

@@ -11,7 +11,7 @@ import customPlaceholderExpression from '!/enterprise/organization-management/cu
 
 Custom Placeholders are designed for cases when the source texts contain some less common placeholders that are not highlighted in the source strings (in the Editor) by default.
 
-## Configure your Custom Placeholders
+## Configure Your Custom Placeholders
 
 You can manage Custom Placeholders in the **Organization Settings**.
 
@@ -28,7 +28,7 @@ You can manage Custom Placeholders in the **Organization Settings**.
 
 Once the custom placeholders are assigned to the project, project members will see them highlighted in the Editor during the translation process.
 
-## Custom placeholders syntax elements
+## Understanding the Syntax: A Simple Example
 
 To configure your custom placeholder expression, you can use the elements from [the expression syntax table](/enterprise/expression-syntax-elements/).
 
@@ -62,7 +62,7 @@ To simplify things a bit, let's deconstruct the expression above.
   />
 </CardGrid>
 
-## Custom Placeholder expression examples
+## Custom Placeholder Expression Examples
 
 Below you can see a few examples of custom placeholder expression and how they will be highlighted in source strings in the Editor.
 
@@ -84,6 +84,16 @@ Expression:
 start, maybe "(", then "%", then "{", anything,  then "}", maybe ")", then "%", end
 ```
 
+This expression deconstructed:
+
+* `maybe "("` &ndash; Allows the placeholder to optionally start with a `(`.
+* `then "%"` &ndash; Requires a `%` character.
+* `then "{"` &ndash; Requires a `{` character.
+* `anything` &ndash; Matches any character or sequence of characters inside the placeholder.
+* `then "}"` &ndash; Requires a `}` character.
+* `maybe ")"` &ndash; Allows the placeholder to optionally end with a `)`.
+* `then "%"` &ndash; Requires a `%` character.
+
 ##### Custom placeholder enclosed in double square brackets
 
 String example:
@@ -98,6 +108,13 @@ Expression:
 start, then "[[", anythingbut "[[", then "]]", multiple, end
 ```
 
+This expression deconstructed:
+
+* `then "[["` &ndash; Requires the placeholder to start with `[[`.
+* `anythingbut "[["` &ndash; Matches any character *except* the opening `[[` brackets.
+* `then "]]"` &ndash; Requires the placeholder to end with `]]`.
+* `multiple` &ndash; Allows the pattern (the content inside the brackets) to repeat.
+
 ##### Custom placeholder
 
 String example:
@@ -137,5 +154,5 @@ A test string with a Long sentence that you might want to highlight as a single
 Expression:
 
 ```graphql wrap
-start, then "Long sentence that you might want to highlight as a single custom placeholder"
+start, then "Long sentence that you might want to highlight as a single custom placeholder", end
 ```