This is the hidden input value:
<input type="hidden" name="#raw_file" value="true">
The value="true" could be programmatically changed so a file can be parsed or not parsed in the same page code.
A php warning occurs when a text area is to be saved to a file and it contains a reserved php character. Update.php tries to parse the file and extract a specific section even if the file is only to be saved. It is also trying to extract a section when the $section is not defined i.e. $section is set to false.
