patch 8.2.2677: Vim9: cannot use only some of the default arguments

Problem:    Vim9: cannot use only some of the default arguments.
Solution:   Use v:none to use default argument value.  Remove
            uf_def_arg_idx[], use JUMP_IF_ARG_SET. (closes #6504)

runtime/doc/vim9.txt

@@ -125,6 +125,10 @@ that starts a comment: >
 	var name = value # comment
 	var name = value# error!
 
+Do not start a comment with #{, it looks like the legacy dictionary literal
+and produces an error where this might be confusing.  #{{ or #{{{ are OK,
+these can be used to start a fold.
+
 In legacy Vim script # is also used for the alternate file name.  In Vim9
 script you need to use %% instead.  Instead of ## use %%% (stands for all
 arguments).
@@ -164,6 +168,15 @@ list type, similar to TypeScript.  For example, a list of numbers: >
 	   for item in itemlist
 	     ...
 
+When a function argument is optional (it has a default value) passing `v:none`
+as the argument results in using the default value.  This is useful when you
+want to specify a value for an argument that comes after an argument that
+should use its default value.  Example: >
+	def MyFunc(one = 'one', last = 'last)
+	  ...
+	enddef
+	MyFunc(v:none, 'LAST')  # first argument uses default value 'one'
+
 
 Functions and variables are script-local by default ~
 							*vim9-scopes*
@@ -190,6 +203,12 @@ search for the function:
 However, it is recommended to always use "g:" to refer to a global function
 for clarity.
 
+Since a script-local function reference can be used without "s:" the name must
+start with an upper case letter even when using the ":s" prefix.  In legacy
+script "s:funcref" could be used, because it could not be referred to with
+"funcref".  In Vim9 script it can, therefore "s:Funcref" must be used to avoid
+that the name interferes with builtin functions.
+
 In all cases the function must be defined before used.  That is when it is
 called, when `:defcompile` causes it to be compiled, or when code that calls
 it is being compiled (to figure out the return type).
@@ -279,6 +298,9 @@ without any command.  The same for global, window, tab, buffer and Vim
 variables, because they are not really declared.  They can also be deleted
 with `:unlet`.
 
+`:lockvar` does not work on local variables.  Use `:const` and `:final`
+instead.
+
 Variables, functions and function arguments cannot shadow previously defined
 or imported variables and functions in the same script file.
 Variables may shadow Ex commands, rename the variable if needed.
@@ -409,7 +431,18 @@ Additionally, a lambda can contain statements in {}: >
 		g:was_called = 'yes'
 		return expression
 	    }
-NOT IMPLEMENTED YET
+
+The ending "}" must be at the start of a line.  It can be followed by other
+characters, e.g.: >
+	var d = mapnew(dict, (k, v): string => {
+	     return 'value'
+	   })
+No command can follow the "{", only a comment can be used there.
+
+Rationale: The "}" cannot be after a command because it would require parsing
+the commands to find it.  For consistency with that no command can follow the
+"{".  Unfortunately this means using "() => {  command  }" does not work, line
+breaks are always required.
 
 							*vim9-curly*
 To avoid the "{" of a dictionary literal to be recognized as a statement block
@@ -705,6 +738,7 @@ In legacy script this results in the character 0xc3 (an illegal byte), in Vim9
 script this results in the string 'á'.
 A negative index is counting from the end, "[-1]" is the last character.
 To exclude the last character use |slice()|.
+To count composing characters separately use |strcharpart()|.
 If the index is out of range then an empty string results.
 
 In legacy script "++var" and "--var" would be silently accepted and have no
@@ -972,6 +1006,8 @@ And classes and interfaces can be used as types: >
 	:var mine: MyInterface<string>
 {not implemented yet}
 
+You may also find this wiki useful.  It was written by an early adoptor of
+Vim9 script: https://github.com/lacygoill/wiki/blob/master/vim/vim9.md
 
 Variable types and type casting	~
 							*variable-types*
@@ -1044,6 +1080,27 @@ to a list of numbers.
 Same for |extend()|, use |extendnew()| instead, and for |flatten()|, use
 |flattennew()| instead.
 
+Closures defined in a loop will share the same context.  For example: >
+	var flist: list<func>
+	for i in range(10)
+	  var inloop = i
+	  flist[i] = () => inloop
+	endfor
+
+The "inloop" variable will exist only once, all closures put in the list refer
+to the same instance, which in the end will have the value 9.  This is
+efficient.  If you do want a separate context for each closure call a function
+to define it: >
+	def GetFunc(i: number): func
+	  var inloop = i
+	  return () => inloop
+	enddef
+
+	var flist: list<func>
+	for i in range(10)
+	  flist[i] = GetFunc(i)
+	endfor
+
 ==============================================================================
 
 5. Namespace, Import and Export