Update runtime files

runtime/doc/vim9.txt

@@ -1,4 +1,4 @@
-*vim9.txt*	For Vim version 8.2.  Last change: 2020 Apr 03
+*vim9.txt*	For Vim version 8.2.  Last change: 2020 Apr 09
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -120,6 +120,13 @@ and without `:let`, because there is no rule about where they are declared.
 Variables cannot shadow previously defined variables.
 Variables may shadow Ex commands, rename the variable if needed.
 
+Global variables must be prefixed with "g:", also at the script level.
+However, global user defined functions are used without "g:". >
+	vim9script
+	let script_local = 'text'
+	let g:global = 'value'
+	let Funcref = ThatFunction
+
 Since "&opt = value" is now assigning a value to option "opt", ":&" cannot be
 used to repeat a `:substitute` command.
 
@@ -156,6 +163,18 @@ since the function has to be looked up by name.  And a typo in the function
 name will only be found when the call is executed.
 
 
+Omitting function() ~
+
+A user defined function can be used as a function reference in an expression
+without `function()`. The argument types and return type will then be checked.
+The function must already have been defined. >
+
+	let Funcref = MyFunction
+
+When using `function()` the resulting type is "func", a function with any
+number of arguments and any return type.  The function can be defined later.
+
+
 No curly braces expansion ~
 
 |curly-braces-names| cannot be used.
@@ -213,8 +232,7 @@ few exceptions.
 	blob		non-empty
 	list		non-empty (different from JavaScript)
 	dictionary	non-empty (different from JavaScript)
-	func		when not NULL
-	partial		when not NULL
+	func		when there is a function name
 	special		v:true
 	job		when not NULL
 	channel		when not NULL
@@ -301,6 +319,7 @@ The following builtin types are supported:
 	job
 	channel
 	func
+	func: {type}
 	func({type}, ...)
 	func({type}, ...): {type}
 
@@ -318,12 +337,22 @@ memory.
 
 A partial and function can be declared in more or less specific ways:
 func				any kind of function reference, no type
-				checking
+				checking for arguments or return value
 func: {type}			any number and type of arguments with specific
 				return type
-func({type} ...)		function with argument types, does not return
+func({type})			function with argument type, does not return
 				a value
-func({type} ...): {type}	function with argument types and return type
+func({type}): {type}		function with argument type and return type
+func(?{type})			function with type of optional argument, does
+				not return a value
+func(...{type})			function with type of variable number of
+				arguments, does not return a value
+func({type}, ?{type}, ...{type}): {type}
+				function with:
+				- type of mandatory argument
+				- type of optional argument
+				- type of variable number of arguments
+				- return type
 
 If the return type is "void" the function does not return a value.