File Extensions dialog box
This dialog box appears when you press the Advanced button on the Settings & Syntax page of the Preferences dialog box. In this dialog box, you can set additional file extension options for the file type.File extensions
Specify file extensions for current file type. You must separate each extension by semicolon(;). For example, HTML file type has following extensions - html;htm;asp;shtml
An additional file nameSpecify an additional file name in case the file type is not based on file extensions. You can include the wildcard * ? in this file name.
First line of fileSpecify the content of first line of file if the file type is based on the first line of file.