initial crack at :command -complete - YALNS

locale/en-US/map.txt

@@ -286,6 +286,40 @@ The valid values are:
 *-nargs=+* One or more argument is allowd
 --------------------------------------------------------------------------------
 
+|E180| |E181| |:command-complete| +
+Argument completion
+
+Completion for arguments to user defined commands is not available by default.
+Completion can be enabled by specifying one of the following arguments to the
+-complete option when defining the command.
+`----------------`--------------------------------------------------------------
+*bookmark*       bookmarks
+*buffer*         buffers
+*command*        Ex commands
+*environment*    environment variables
+*event*          autocommand events
+*file*           files
+*help*           help tags
+*javascript*     javascript
+*mapping*        user mappings
+*shellcmd*       shell commands
+*url*            URLs
+*custom,{func}*  custom completion, provided by {func} 
+--------------------------------------------------------------------------------
+
+|E467| |E468| |:command-completion-custom| +
+Custom completion
+
+Custom completion can be provided by specifying the "custom,{func}" argument to
+-complete. The {func} is called with one argument, the word being completed,
+and should return an array [start, completions].
+
+*start* is the index into the word being completed at which the returned values
+should be applied and *completions* is a two dimensional array of the form:
+\[[arg1, description1], [arg2, description2], ...]
+
+// TODO: add examples
+
 |E177| |E178| |:command-count| +
 Count handling