Implement proper folding support

doc/tagbar.txt

@@ -606,10 +606,6 @@ files.
     problem in practice anyway. Tags with the same name at any other level are
     no problem, though.
 
-  - The fold state of the Tagbar window is lost when the window is left.
-    Again, I don't know of any proper way around this that still allows
-    auto-updating -- |winsaveview()| doesn't really help here.
-
 ==============================================================================
 8. History						*tagbar-history*
 
@@ -659,5 +655,7 @@ warranty of any kind, either expressed or implied. In no event will the
 copyright holder be liable for any damamges resulting from the use of this
 software.
 
+The folding technique was inspired by NERDTree by Martin Grenfell.
+
 ==============================================================================
  vim: tw=78 ts=8 sw=8 sts=8 noet ft=help

syntax/tagbar.vim

@@ -9,19 +9,30 @@ if exists("b:current_syntax")
   finish
 endif
 
-syntax match Comment    '^" .*'             " Comments
-syntax match Identifier '^ [^: ]\+[^:]\+$'  " Non-scoped kinds
-syntax match Title      '[^(* ]\+\ze\*\? :' " Scope names
-syntax match Type       ' : \zs.*'          " Scope types
-syntax match SpecialKey '(.*)'              " Signatures
-syntax match NonText    '\*\ze :'           " Pseudo-tag identifiers
+syntax match TagbarComment   '^".*'
+
+syntax match TagbarKind      '\([-+][-+ ]\)\@<=[^-+: ]\+[^:]\+$'
+syntax match TagbarScope     '[^-+#(* ]\+\(\*\? :\)\@='
+syntax match TagbarScopeType ' : \zs.*'
+syntax match TagbarSignature '(.*)'
+syntax match TagbarPseudoID  '\*\ze :'
+
+syntax match TagbarFoldIcon  '[-+]\([-+# ]\)\@='
+
+syntax match TagbarAccessPublic    '\([-+ ]\)\@<=+\([^-+# ]\)\@='
+syntax match TagbarAccessProtected '\([-+ ]\)\@<=#\([^-+# ]\)\@='
+syntax match TagbarAccessPrivate   '\([-+ ]\)\@<=-\([^-+# ]\)\@='
+
+highlight default link TagbarComment   Comment
+highlight default link TagbarKind      Identifier
+highlight default link TagbarScope     Title
+highlight default link TagbarScopeType Type
+highlight default link TagbarSignature SpecialKey
+highlight default link TagbarPseudoID  NonText
+highlight default link TagbarFoldIcon  FoldColumn
 
 highlight default TagbarAccessPublic    guifg=Green ctermfg=Green
 highlight default TagbarAccessProtected guifg=Blue  ctermfg=Blue
 highlight default TagbarAccessPrivate   guifg=Red   ctermfg=Red
 
-syntax match TagbarAccessPublic    '^\s*+\ze[^ ]'
-syntax match TagbarAccessProtected '^\s*#\ze[^ ]'
-syntax match TagbarAccessPrivate   '^\s*-\ze[^ ]'
-
 let b:current_syntax = "tagbar"