+OPERATION is either nil or a string that names a supported operation.
+What operations can be used depends on the particular DOCUMENT and its
+handler application, but typically it is one of the following common
+operations:
+
+ \"open\" - open DOCUMENT, which could be a file, a directory, or an
+ executable program. If it is an application, that
+ application is launched in the current buffer's default
+ directory. Otherwise, the application associated with
+ DOCUMENT is launched in the buffer's default directory.
+ \"print\" - print DOCUMENT, which must be a file
+ \"explore\" - start the Windows Explorer on DOCUMENT
+ \"edit\" - launch an editor and open DOCUMENT for editing; which
+ editor is launched depends on the association for the
+ specified DOCUMENT
+ \"find\" - initiate search starting from DOCUMENT which must specify
+ a directory
+ nil - invoke the default OPERATION, or \"open\" if default is
+ not defined or unavailable
+
+DOCUMENT is typically the name of a document file or a URL, but can
+also be a program executable to run, or a directory to open in the
+Windows Explorer.
+
+If DOCUMENT is a program executable, the optional arg PARAMETERS can
+be a string containing command line parameters that will be passed to
+the program; otherwise, PARAMETERS should be nil or unspecified.
+
+Second optional argument SHOW-FLAG can be used to control how the
+application will be displayed when it is invoked. If SHOW-FLAG is nil
+or unspceified, the application is displayed normally, otherwise it is
+an integer representing a ShowWindow flag: