-instance of FILE or TABLE can be followed by DROP, KEEP, and/or RENAME
-subcommands. These take the same form as the corresponding subcommands
-of @cmd{GET} (@pxref{GET}), and perform the same functions.
+instance of FILE or TABLE can be followed by any sequence of DROP,
+KEEP, or RENAME subcommands. These have the same form and meaning as
+the corresponding subcommands of @cmd{GET} (@pxref{GET}), but apply
+only to variables in the given file.
+
+Each FILE or TABLE may optionally be followed by an IN subcommand,
+which creates a numeric variable with the specified name and format
+F1.0. The IN variable takes value 1 in a case if the given file
+contributed a row to the merged file, 0 otherwise. The DROP, KEEP,
+and RENAME subcommands do not affect IN variables.