The three-character filename extension associates all of the runtime solution files with the runtime application. If a user has more than one runtime database solution on a machine, the filename extension together with the binding key will ensure that the correct runtime application is started when a solution file is double-clicked. Use an extension that is unique to your users’ computer systems.
The Developer Utilities automatically update all files to use the three-character extension that you specify and append the extension to the filenames. FileMaker data source references used in relationships, scripts, and external value lists are updated to interact with the new filenames.
The three-character extension registers your runtime application with the Windows operating system. The extension is used by Windows to determine which application starts when you double-click a solution file. The Developer Utilities append the extension to all database filenames in the runtime database solution during the binding process.
In the Mac OS X, the three-character extension becomes the creator code for the runtime application. The creator code must be unique to ensure that the Mac OS X Finder can determine which application created each document. The creator code is stored in the solution files and in the runtime application.
Because creator codes are four characters, the Developer Utilities insert an uppercase “F” after the first character. For example, the default three-character extension “USR” becomes the “UFSR” creator code. Creator codes are case-sensitive.
If the three-character extension is not unique, it might cause registry conflicts in Windows. For example, if you use the .fp7 extension for your runtime database solution and your users have FileMaker Pro installed on their hard disks, all of their FileMaker Pro document icons will change to the runtime icons. Additionally, FileMaker Pro documents will no longer automatically open the FileMaker Pro application.