--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 8.2.  Last change: 2022 Jun 05
+*builtin.txt*	For Vim version 8.2.  Last change: 2022 Jun 16
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -8809,6 +8809,8 @@ strcharpart({src}, {start} [, {len} [, {
 			strcharpart('abc', -1, 2)
 <		results in 'a'.
 
+		Returns an empty string on error.
+
 		Can also be used as a |method|: >
 			GetText()->strcharpart(5)
 
@@ -8821,6 +8823,8 @@ strchars({string} [, {skipcc}])					*str
 		When {skipcc} set to 1, Composing characters are ignored.
 		|strcharlen()| always does this.
 
+		Returns zero on error.
+
 		Also see |strlen()|, |strdisplaywidth()| and |strwidth()|.
 
 		{skipcc} is only available after 7.4.755.  For backward
@@ -8853,6 +8857,7 @@ strdisplaywidth({string} [, {col}])			*s
 		'tabstop' and 'display'.
 		When {string} contains characters with East Asian Width Class
 		Ambiguous, this function's return value depends on 'ambiwidth'.
+		Returns zero on error.
 		Also see |strlen()|, |strwidth()| and |strchars()|.
 
 		Can also be used as a |method|: >
@@ -8886,6 +8891,7 @@ strgetchar({str}, {index})				*strgetcha
 		index.  Composing characters are considered separate
 		characters here.  Use |nr2char()| to convert the Number to a
 		String.
+		Returns -1 if {index} is invalid.
 		Also see |strcharpart()| and |strchars()|.
 
 		Can also be used as a |method|: >
@@ -8940,7 +8946,7 @@ strlen({string})						*strlen()*
 		The result is a Number, which is the length of the String
 		{string} in bytes.
 		If the argument is a Number it is first converted to a String.
-		For other types an error is given.
+		For other types an error is given and zero is returned.
 		If you want to count the number of multibyte characters use
 		|strchars()|.
 		Also see |len()|, |strdisplaywidth()| and |strwidth()|.
@@ -8971,6 +8977,8 @@ strpart({src}, {start} [, {len} [, {char
 		example, to get the character under the cursor: >
 			strpart(getline("."), col(".") - 1, 1, v:true)
 <
+		Returns an empty string on error.
+
 		Can also be used as a |method|: >
 			GetText()->strpart(5)
 
@@ -9033,6 +9041,8 @@ strtrans({string})					*strtrans()*
 <		This displays a newline in register a as "^@" instead of
 		starting a new line.
 
+		Returns an empty string on error.
+
 		Can also be used as a |method|: >
 			GetString()->strtrans()
 
@@ -9042,6 +9052,7 @@ strwidth({string})					*strwidth()*
 		cell, alternatively use |strdisplaywidth()|.
 		When {string} contains characters with East Asian Width Class
 		Ambiguous, this function's return value depends on 'ambiwidth'.
+		Returns zero on error.
 		Also see |strlen()|, |strdisplaywidth()| and |strchars()|.
 
 		Can also be used as a |method|: >
@@ -9067,6 +9078,8 @@ submatch({nr} [, {list}])			*submatch()*
 		When substitute() is used recursively only the submatches in
 		the current (deepest) call can be obtained.
 
+		Returns an empty string or list on error.
+
 		Examples: >
 			:s/\d\+/\=submatch(0) + 1/
 			:echo substitute(text, '\d\+', '\=submatch(0) + 1', '')
@@ -9117,7 +9130,9 @@ substitute({string}, {pat}, {sub}, {flag
 		|submatch()| returns.  Example: >
 		   :echo substitute(s, '%\(\x\x\)', {m -> '0x' .. m[1]}, 'g')
 
-<		Can also be used as a |method|: >
+<		Returns an empty string on error.
+
+		Can also be used as a |method|: >
 			GetString()->substitute(pat, sub, flags)
 
 swapinfo({fname})					*swapinfo()*
@@ -9172,6 +9187,8 @@ synID({lnum}, {col}, {trans})				*synID(
 		Warning: This function can be very slow.  Best speed is
 		obtained by going through the file in forward direction.
 
+		Returns zero on error.
+
 		Example (echoes the name of the syntax item under the cursor): >
 			:echo synIDattr(synID(line("."), col("."), 1), "name")
 <
@@ -9209,6 +9226,8 @@ synIDattr({synID}, {what} [, {mode}])			
 		"undercurl"	"1" if undercurled
 		"strike"	"1" if strikethrough
 
+		Returns an empty string on error.
+
 		Example (echoes the color of the syntax item under the
 		cursor): >
 	:echo synIDattr(synIDtrans(synID(line("."), col("."), 1)), "fg")
@@ -9223,6 +9242,8 @@ synIDtrans({synID})					*synIDtrans()*
 		highlight the character.  Highlight links given with
 		":highlight link" are followed.
 
+		Returns zero on error.
+
 		Can also be used as a |method|: >
 	:echo synID(line("."), col("."), 1)->synIDtrans()->synIDattr("fg")
 
@@ -9267,7 +9288,7 @@ synstack({lnum}, {col})					*synstack()*
 			   echo synIDattr(id, "name")
 			endfor
 <		When the position specified with {lnum} and {col} is invalid
-		nothing is returned.  The position just after the last
+		an empty List is returned.  The position just after the last
 		character in a line and the first column in an empty line are
 		valid positions.
 
@@ -9381,6 +9402,8 @@ tabpagenr([{arg}])					*tabpagenr()*
 				previous tab page 0 is returned.
 		The number can be used with the |:tab| command.
 
+		Returns zero on error.
+
 
 tabpagewinnr({tabarg} [, {arg}])			*tabpagewinnr()*
 		Like |winnr()| but for tab page {tabarg}.
@@ -9453,6 +9476,7 @@ tan({expr})						*tan()*
 		Return the tangent of {expr}, measured in radians, as a |Float|
 		in the range [-inf, inf].
 		{expr} must evaluate to a |Float| or a |Number|.
+		Returns 0.0 if {expr} is not a |Float| or a |Number|.
 		Examples: >
 			:echo tan(10)
 <			0.648361 >
@@ -9469,6 +9493,7 @@ tanh({expr})						*tanh()*
 		Return the hyperbolic tangent of {expr} as a |Float| in the
 		range [-1, 1].
 		{expr} must evaluate to a |Float| or a |Number|.
+		Returns 0.0 if {expr} is not a |Float| or a |Number|.
 		Examples: >
 			:echo tanh(0.5)
 <			0.462117 >
@@ -9598,6 +9623,8 @@ timer_start({time}, {callback} [, {optio
 				Vim becomes unusable because of all the error
 				messages.
 
+		Returns -1 on error.
+
 		Example: >
 			func MyHandler(timer)
 			  echo 'Handler called'
@@ -9633,7 +9660,7 @@ timer_stopall()						*timer_stopall()*
 tolower({expr})						*tolower()*
 		The result is a copy of the String given, with all uppercase
 		characters turned into lowercase (just like applying |gu| to
-		the string).
+		the string).  Returns an empty string on error.
 
 		Can also be used as a |method|: >
 			GetText()->tolower()
@@ -9641,7 +9668,7 @@ tolower({expr})						*tolower()*
 toupper({expr})						*toupper()*
 		The result is a copy of the String given, with all lowercase
 		characters turned into uppercase (just like applying |gU| to
-		the string).
+		the string).  Returns an empty string on error.
 
 		Can also be used as a |method|: >
 			GetText()->toupper()
@@ -9654,6 +9681,8 @@ tr({src}, {fromstr}, {tostr})				*tr()*
 		and so on.  Exactly like the unix "tr" command.
 		This code also deals with multibyte characters properly.
 
+		Returns an empty string on error.
+
 		Examples: >
 			echo tr("hello there", "ht", "HT")
 <		returns "Hello THere" >
@@ -9679,6 +9708,7 @@ trim({text} [, {mask} [, {dir}]])				*tr
 		When omitted both ends are trimmed.
 
 		This function deals with multibyte characters properly.
+		Returns an empty string on error.
 
 		Examples: >
 			echo trim("   some text ")
@@ -9697,6 +9727,7 @@ trunc({expr})							*trunc()*
 		Return the largest integral value with magnitude less than or
 		equal to {expr} as a |Float| (truncate towards zero).
 		{expr} must evaluate to a |Float| or a |Number|.
+		Returns 0.0 if {expr} is not a |Float| or a |Number|.
 		Examples: >
 			echo trunc(1.456)
 <			1.0  >
@@ -9815,12 +9846,15 @@ uniq({list} [, {func} [, {dict}]])			*un
 <		The default compare function uses the string representation of
 		each item.  For the use of {func} and {dict} see |sort()|.
 
+		Returns zero if {list} is not a |List|.
+
 		Can also be used as a |method|: >
 			mylist->uniq()
 
 values({dict})						*values()*
 		Return a |List| with all the values of {dict}.  The |List| is
 		in arbitrary order.  Also see |items()| and |keys()|.
+		Returns zero if {dict} is not a |Dict|.
 
 		Can also be used as a |method|: >
 			mydict->values()
@@ -9988,6 +10022,8 @@ win_gettype([{nr}])					*win_gettype()*
 		popup window then 'buftype' is "terminal" and win_gettype()
 		returns "popup".
 
+		Return an empty string if the window cannot be found.
+
 		Can also be used as a |method|: >
 			GetWinid()->win_gettype()
 <
@@ -10025,6 +10061,8 @@ win_move_separator({nr}, {offset})			*wi
 		specified (e.g., as a consequence of maintaining
 		'winminwidth'). Returns TRUE if the window can be found and
 		FALSE otherwise.
+		This will fail for the rightmost window and a full-width
+		window, since it has no separator on the right.
 
 		Can also be used as a |method|: >
 			GetWinnr()->win_move_separator(offset)