Rename some "python3" symbols to "py3", as the command name.

Documentation updates.

runtime/doc/eval.txt

@@ -1474,10 +1474,11 @@ v:lc_time	The current locale setting for time messages of the runtime
 		command.  See |multi-lang|.
 
 						*v:lnum* *lnum-variable*
-v:lnum		Line number for the 'foldexpr' |fold-expr| and 'indentexpr'
-		expressions, tab page number for 'guitablabel' and
-		'guitabtooltip'.  Only valid while one of these expressions is
-		being evaluated.  Read-only when in the |sandbox|.
+v:lnum		Line number for the 'foldexpr' |fold-expr|, 'formatexpr' and
+		'indentexpr' expressions, tab page number for 'guitablabel'
+		and 'guitabtooltip'.  Only valid while one of these
+		expressions is being evaluated.  Read-only when in the
+		|sandbox|.
 
 					*v:mouse_win* *mouse_win-variable*
 v:mouse_win	Window number for a mouse click obtained with |getchar()|.
@@ -8246,11 +8247,11 @@ missing: >
 ==============================================================================
 11. The sandbox					*eval-sandbox* *sandbox* *E48*
 
-The 'foldexpr', 'includeexpr', 'indentexpr', 'statusline' and 'foldtext'
-options are evaluated in a sandbox.  This means that you are protected from
-these expressions having nasty side effects.  This gives some safety for when
-these options are set from a modeline.	It is also used when the command from
-a tags file is executed and for CTRL-R = in the command line.
+The 'foldexpr', 'formatexpr', 'includeexpr', 'indentexpr', 'statusline' and
+'foldtext' options may be evaluated in a sandbox.  This means that you are
+protected from these expressions having nasty side effects.  This gives some
+safety for when these options are set from a modeline.  It is also used when
+the command from a tags file is executed and for CTRL-R = in the command line.
 The sandbox is also used for the |:sandbox| command.
 
 These items are not allowed in the sandbox:

runtime/doc/if_pyth.txt

@@ -16,8 +16,10 @@ The Python Interface to Vim				*python* *Python*
 
 {Vi does not have any of these commands}
 
-The Python interface is available only when Vim was compiled with the
+The Python 2.x interface is available only when Vim was compiled with the
 |+python| feature.
+The Python 3 interface is available only when Vim was compiled with the
+|+python3| feature.
 
 ==============================================================================
 1. Commands						*python-commands*
@@ -333,7 +335,7 @@ sure edit "gvim.exe" and search for "python\d*.dll\c".
 
 Python 3 support can exist next to Python 2.x.
 
-*:py3* *:python3* *:py3file*
+*:py3* *:py3file*
 
 TODO
 

runtime/doc/index.txt

@@ -1382,6 +1382,8 @@ The commands are sorted on the non-optional part of their name.
 |:ptselect|	:pts[elect]	|:tselect| and show tag in preview window
 |:put|		:pu[t]		insert contents of register in the text
 |:pwd|		:pw[d]		print current directory
+|:py3|		:py3		execute Python 3 command
+|:p3yfile|	:py3f[ile]	execute Python 3 script file
 |:python|	:py[thon]	execute Python command
 |:pyfile|	:pyf[ile]	execute Python script file
 |:quit|		:q[uit]		quit current window (when one window quit Vim)

runtime/doc/options.txt

@@ -3125,12 +3125,15 @@ A jump table for the options with a short description can be found at |Q_op|.
 			{not available when compiled without the |+eval|
 			feature}
 	Expression which is evaluated to format a range of lines for the |gq|
-	operator.  When this option is empty 'formatprg' is used.
+	operator or automatic formatting (see 'formatoptions').  When this
+	option is empty 'formatprg' is used.
 
 	The |v:lnum|  variable holds the first line to be formatted.
 	The |v:count| variable holds the number of lines to be formatted.
 	The |v:char|  variable holds the character that is going to be
-		      inserted.  This can be empty.  Don't insert it yet!
+		      inserted if the expression is being evaluated due to
+		      automatic formatting.  This can be empty.  Don't insert
+		      it yet!
 
 	Example: >
 		:set formatexpr=mylang#Format()