diff --git a/runtime/syntax/testdir/input/vim9_comment.vim b/runtime/syntax/testdir/input/vim9_comment.vim
index fd6a5d2..7d22f46 100644
--- a/runtime/syntax/testdir/input/vim9_comment.vim
+++ b/runtime/syntax/testdir/input/vim9_comment.vim
@@ -34,6 +34,10 @@
   \ continuing comment
   \ continuing comment
 
+var foo = 42 # commment
+  \ continuing comment
+  \ continuing comment
+
 # :Foo
       \ arg1
       #\ comment
diff --git a/runtime/syntax/testdir/input/vim_comment.vim b/runtime/syntax/testdir/input/vim_comment.vim
index f382f8d..2ca6787 100644
--- a/runtime/syntax/testdir/input/vim_comment.vim
+++ b/runtime/syntax/testdir/input/vim_comment.vim
@@ -31,6 +31,10 @@
   \ continuing comment
   \ continuing comment
 
+let foo = 42 " commment
+  \ continuing comment
+  \ continuing comment
+
 " :Foo
       \ arg1
       "\ comment
diff --git a/runtime/syntax/testdir/input/vim_ex_augroup.vim b/runtime/syntax/testdir/input/vim_ex_augroup.vim
index aa13d97..7f7f346 100644
--- a/runtime/syntax/testdir/input/vim_ex_augroup.vim
+++ b/runtime/syntax/testdir/input/vim_ex_augroup.vim
@@ -40,10 +40,17 @@
 augroup  \"\| | autocmd! | augroup END
 augroup! \"\|
 
-" FIXME: required comment prefix
-augroup  foo"comment    " start bad fold
+
+augroup  foo"comment
+  au!
+  au BufRead * echo "Foo"
+augroup END"comment
+
 augroup  foo|echo "Foo"
-augroup END             " terminate bad fold
+  au!
+  au BufRead * echo "Foo"
+augroup END|echo "Foo"
+
 augroup! foo"comment
 augroup! foo|echo "Foo"
 
diff --git a/runtime/syntax/testdir/input/vim_ex_substitute.vim b/runtime/syntax/testdir/input/vim_ex_substitute.vim
index 021060a..7ffd16d 100644
--- a/runtime/syntax/testdir/input/vim_ex_substitute.vim
+++ b/runtime/syntax/testdir/input/vim_ex_substitute.vim
@@ -124,7 +124,6 @@
 
 " Trailing comment and bar
 
-" FIXME: trailing comment, no whitespace
 s" comment
 s| echo "Foo"
 
diff --git a/runtime/syntax/testdir/input/vim_expr.vim b/runtime/syntax/testdir/input/vim_expr.vim
index bb7366d..e58450e 100644
--- a/runtime/syntax/testdir/input/vim_expr.vim
+++ b/runtime/syntax/testdir/input/vim_expr.vim
@@ -4,6 +4,15 @@
 echo 'tab: \t, new line: \n, backslash: \\'
 echo "tab: \t, new line: \n, backslash: \\"
 
+" string starts immediately after line continuation character - tests a
+" comment/string distinguishing implementation quirk
+echo "foo"
+      \"bar"
+      \ "baz"
+echo 'foo'
+      \'bar'
+      \ 'baz'
+
 " String escape sequences
 
 echo "\316 - \31 - \3 - \x1f - \xf - \X1F - \XF - \u02a4 - \U000002a4 - \b - \e - \f - \n - \r - \t - \\ - \" - \<C-W>"
@@ -21,6 +30,13 @@
 echo "\<C->>>"
 echo "\<*C->>>"
 
+echo ""
+echo "\""
+echo "foo\""
+echo "\"foo"
+echo "foo\"bar"
+
+echo ''
 echo ''''
 echo '''foo'
 echo 'foo'''
@@ -30,6 +46,7 @@
 " https://github.com/tpope/vim-unimpaired/blob/6d44a6dc2ec34607c41ec78acf81657248580bf1/plugin/unimpaired.vim#L232
 let cmd = 'put!=repeat(nr2char(10), v:count1)|silent '']+'
 
+
 " String interpolation
 
 echo 'Don''t highlight interpolation: {{ {1 + 2} }}'
@@ -39,10 +56,61 @@
 echo $"Highlight interpolation:\t{{ { string({"foo": "bar"}) } }}"
 echo $"Highlight interpolation:\t{{ { $"nested: {{ {1 + 2} }}" } }}"
 
-echo $''''
-echo $'''foo'
-echo $'foo'''
-echo $'foo''bar'
+
+" Continued string
+
+let s = "
+      "\ comment
+      \ part 1
+      "\ comment
+      \ part 2
+      "\ comment
+      \" " tail comment
+
+let s = "\"
+      \\" part 1 \"
+      "\ escape sequence
+      \ \"part 2\"
+      \\"" " tail comment
+
+let s = '
+      "\ comment
+      \ part 1
+      "\ comment
+      \ part 2
+      "\ comment
+      \' " tail comment
+
+let s = '''
+      \'' part 1 ''
+      "\ escape sequence
+      \ ''part 2''
+      \''' " tail comment
+
+let s = $"
+      "\ comment
+      \ part 1
+      "\ comment
+      \ part 2
+      "\ comment
+      \" " tail comment
+
+let s = $'
+      "\ comment
+      \ part 1
+      "\ comment
+      \ part 2
+      "\ comment
+      \' " tail comment
+
+call strlen("part 1
+      "\ comment
+      \ part 2")
+
+call append(0, "part 1
+      "\ comment
+      \ part 2")
+
 
 " Number
 
@@ -301,12 +369,17 @@
       \ bar +
       \ "baz"
 
+let foo = foo +
+      "\ "comment string"
+      \ bar
+
 " Function calls
 
 call Foo(v:true, v:false, v:null)
 
 
 " Issue #16221 (vimString becomes vimVar when preceded by !)
+
 let bar = !'g:bar'->exists()