Each Exec field may take a number of arguments which will be
      expanded by the file manager or program launcher and passed to the
      program if necessary.
    
      Literal % characters must be escaped as %%, and adding new
      format characters is not allowed. It's a fatal error to have an
      Exec field with a format character not given in the spec (exception
      to this are the deprecated format characters which can be ignored,
      that is expanded to no parameters, by the implementation).
      Again for emphasis: nonstandard extensions are 
      not allowed here - you must add an X-Foo-Exec field if you have
      nonstandard Exec lines.
    
The escaping of the exec parameters is done in the way the mailcap specification describes. Take a look at RFC 1524 for more information.
Recognized fields are as follows:
| %f | A single file name, even if multiple files are selected.  The system
	      reading the desktop entry should recognize that the program in
	      question cannot handle multiple file arguments, and it should
	      should probably spawn and execute multiple copies of a program
	      for each selected file if the program is not able to handle
	      additional file arguments. If files are not on the local file system
	      (i.e. are on HTTP or FTP locations), the files will be copied to the local
	      file system and %fwill be expanded to point at the temporary
	      file. Used for programs that do not understand the URL syntax. | 
| %F | A list of files. Use for apps that can open several local files at once. | 
| %u | A single URL. | 
| %U | A list of URLs. | 
| %d | Directory containing the file that would be passed in a %ffield. | 
| %D | List of directories containing the files that would be
              passed in to a %Ffield. | 
| %n | A single filename (without path). | 
| %N | A list of filenames (without paths). | 
| %i | The Iconfield of the desktop entry
              expanded as two parameters, first--iconand then the contents of theIconfield. Should not expand as any
              parameters if theIconfield is empty
              or missing. | 
| %c | The translated Namefield associated with the desktop entry. | 
| %k | The location of the desktop file as either a URI (if for example gotten from the vfolder system) or a local filename or empty if no location is known. | 
| %v | The name of the Deviceentry in the desktop file. |