Custom applications must follow the design rule imposed by the application framework. If the application framework design does not address a particular use case, other custom rules and agents might have to be used. For example, one such limitation is when a user uploads a file, the application that processes the file is determined based on which directory the file is uploaded into. If custom processing should be triggered by a file name or extension, regardless of the directory the file is uploaded into, a general custom rule must be used.