This is a built-in template used for generate declaration of method +sharedInstance into class header section, e.g. when calling the Code | Generate | +sharedInstance function.
The template is editable. Along with Objective-C expressions and comments, you can also use predefined variables that will be then expanded into the corresponding values.
Predefined variables will take the following values:
${$CLASS_TYPE}   name of the class where the method is implemented
All the predefined variables from the C File Header template (Includes tab) are also available (e.g. ${USER}, ${DATE}, etc.)