This is a built-in template used for filling the body of an implemented function when it is generated, e.g. when calling the Code | Implement Functions... function.
The template is editable. Along with 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:
${RETURN_TYPE}   return type of a created function
${DEFAULT_RETURN_VALUE}   value returned by the function by default
All the predefined variables from the C File Header template (Includes tab) are also available (e.g. ${USER}, ${DATE}, etc.)