diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index a66df1e..e5321c5 100644
--- a/runtime/doc/diff.txt
+++ b/runtime/doc/diff.txt
@@ -376,6 +376,9 @@
 'diffopt' option.  'diffexpr' cannot change the value of 'lines' and
 'columns'.
 
+The advantage of using a function call without arguments is that it is faster,
+see |expr-option-function|.
+
 Example (this does almost the same as 'diffexpr' being empty): >
 
 	set diffexpr=MyDiff()
@@ -441,6 +444,9 @@
 	v:fname_diff		patch file
 	v:fname_out		resulting patched file
 
+The advantage of using a function call without arguments is that it is faster,
+see |expr-option-function|.
+
 Example (this does the same as 'patchexpr' being empty): >
 
 	set patchexpr=MyPatch()
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 4ea75ba..aa69dd1 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1626,6 +1626,9 @@
 	Note that v:charconvert_from and v:charconvert_to may be different
 	from 'encoding'.  Vim internally uses UTF-8 instead of UCS-2 or UCS-4.
 
+	The advantage of using a function call without arguments is that it is
+	faster, see |expr-option-function|.
+
 	Encryption is not done by Vim when using 'charconvert'.  If you want
 	to encrypt the file after conversion, 'charconvert' should take care
 	of this.
@@ -3664,6 +3667,9 @@
 <	This will invoke the mylang#Format() function in the
 	autoload/mylang.vim file in 'runtimepath'. |autoload|
 
+	The advantage of using a function call without arguments is that it is
+	faster, see |expr-option-function|.
+
 	The expression is also evaluated when 'textwidth' is set and adding
 	text beyond that limit.  This happens under the same conditions as
 	when internal formatting is used.  Make sure the cursor is kept in the
@@ -4534,11 +4540,14 @@
 
 	If the expression starts with s: or |<SID>|, then it is replaced with
 	the script ID (|local-function|). Example: >
-		set includeexpr=s:MyIncludeExpr(v:fname)
-		set includeexpr=<SID>SomeIncludeExpr(v:fname)
+		set includeexpr=s:MyIncludeExpr()
+		set includeexpr=<SID>SomeIncludeExpr()
 <	Otherwise, the expression is evaluated in the context of the script
 	where the option was set, thus script-local items are available.
 
+	It is more efficient if the value is just a function call without
+	arguments, see |expr-option-function|.
+
 	The expression will be evaluated in the |sandbox| when set from a
 	modeline, see |sandbox-option|.
 	This option cannot be set in a modeline when 'modelineexpr' is off.
@@ -4620,6 +4629,9 @@
 <	Otherwise, the expression is evaluated in the context of the script
 	where the option was set, thus script-local items are available.
 
+	The advantage of using a function call without arguments is that it is
+	faster, see |expr-option-function|.
+
 	The expression must return the number of spaces worth of indent.  It
 	can return "-1" to keep the current indent (this means 'autoindent' is
 	used for the indent).
@@ -7470,9 +7482,11 @@
 			The file is used for all languages.
 
 	expr:{expr}	Evaluate expression {expr}.  Use a function to avoid
-			trouble with spaces.  |v:val| holds the badly spelled
-			word.  The expression must evaluate to a List of
-			Lists, each with a suggestion and a score.
+			trouble with spaces.  Best is to call a function
+			without arguments, see |expr-option-function|.
+			|v:val| holds the badly spelled word.  The expression
+			must evaluate to a List of Lists, each with a
+			suggestion and a score.
 			Example:
 				[['the', 33], ['that', 44]] ~
 			Set 'verbose' and use |z=| to see the scores that the
diff --git a/runtime/doc/print.txt b/runtime/doc/print.txt
index 2774e98..9f8bb20 100644
--- a/runtime/doc/print.txt
+++ b/runtime/doc/print.txt
@@ -158,13 +158,16 @@
 If you change this option, using a function is an easy way to avoid having to
 escape all the spaces.  Example: >
 
-	:set printexpr=PrintFile(v:fname_in)
-	:function PrintFile(fname)
-	:  call system("ghostview " .. a:fname)
-	:  call delete(a:fname)
+	:set printexpr=PrintFile()
+	:function PrintFile()
+	:  call system("ghostview " .. v:fname_in)
+	:  call delete(v:fname_in)
 	:  return v:shell_error
 	:endfunc
 
+It is more efficient if the option is set to just a function call,
+see |expr-option-function|.
+
 Be aware that some print programs return control before they have read the
 file.  If you delete the file too soon it will not be printed.  These programs
 usually offer an option to have them remove the file when printing is done.