Add hierarchy to syntax file

Redo comments with fold markers to provide an appropriate hierarchy to
the syntax file itself.

syntax/snippets.vim

@@ -5,6 +5,8 @@ if exists("b:current_syntax")
   finish
 endif
 
+" Embedded Syntaxes {{{1
+
 syntax include @Python syntax/python.vim
 unlet b:current_syntax
 syntax include @Viml syntax/vim.vim
@@ -12,10 +14,15 @@ unlet b:current_syntax
 syntax include @Shell syntax/sh.vim
 unlet b:current_syntax
 
-" global matches
+" Syntax definitions {{{1
+
+" Comments {{{2
+
 syn match snipComment "^#.*" contains=snipTODO
 syn keyword snipTODO FIXME NOTE NOTES TODO XXX contained
 
+" Miscellaneous {{{2
+
 syn match snipDocString '"[^"]*"$'
 syn match snipString '"[^"]*"'
 syn match snipTabsOnly "^\t\+$"
@@ -23,33 +30,47 @@ syn match snipLeadingSpaces "^\t* \+"
 
 syn match snipKeyword "\(\<\(end\)\?\(snippet\|global\)\>\)\|extends\|clearsnippets\|priority" contained
 
-" extends definitions
+" Extends {{{2
+
 syn match snipExtends "^extends.*" contains=snipKeyword
 
-" snippet definitions
+" Definitions {{{2
+
+" snippet {{{3
+
+syn region snipSnippet fold keepend start="^snippet" end="^endsnippet" contains=snipStart,snipEnd,snipTabsOnly,snipLeadingSpaces,snipCommand,snipVarExpansion,snipVar,snipVisual
+
 syn match snipStart "^snippet.*" contained contains=snipKeyword,snipDocString
 syn match snipEnd "^endsnippet" contained contains=snipKeyword
 
+" Command substitution {{{4
+
 syn region snipCommand keepend matchgroup=snipCommandDelim start="`" skip="\\[{}\\$`]" end="`" contains=snipPythonCommand,snipVimLCommand,snipShellCommand
 syn region snipShellCommand start="\ze\_." skip="\\[{}\\$`]" end="\ze`" contained contains=@Shell
 syn region snipPythonCommand matchgroup=snipPythonCommandP start="`\@<=!p\_s" skip="\\[{}\\$`]" end="\ze`" contained contains=@Python
 syn region snipVimLCommand matchgroup=snipVimLCommandV start="`\@<=!v\_s" skip="\\[{}\\$`]" end="\ze`" contained contains=@Viml
 
+" Variables {{{4
+
 syn match snipVar "\$\d*" contained
 syn region snipVisual matchgroup=Define start="\${VISUAL" end="}" contained
 syn region snipVarExpansion matchgroup=Define start="\${\d*" end="}" contained contains=snipVar,snipVarExpansion,snipCommand
-syn region snippet fold keepend start="^snippet" end="^endsnippet" contains=snipStart,snipEnd,snipTabsOnly,snipLeadingSpaces,snipCommand,snipVarExpansion,snipVar,snipVisual
 
-" global definitions
+" global {{{3
+
 syn match snipGlobalStart "^global.*" contained contains=snipKeyword,snipString
 syn match snipGlobalEnd "^endglobal" contained contains=snipKeyword
 syn region snipGlobal fold keepend start="^global" end="^endglobal" contains=snipGlobalStart,snipGlobalEnd,snipLeadingSpaces,snipTabsOnly,snipCommand,snipVarExpansion,snipVar,@Python
 
-" snippet clearing
+" priority {{{3
-syn match snipClear "^clearsnippets"
+
 syn match snipPriority "^priority"
 
-" highlighting rules
+" Snippt Clearing {{{2
+
+syn match snipClear "^clearsnippets"
+
+" Highlight groups {{{1
 
 hi def link snipComment          Comment
 hi def link snipLeadingSpaces    Error
@@ -75,7 +96,7 @@ hi def link snipVimLCommandV     PreProc
 hi def link snipVar              StorageClass
 hi def link snipVarExpansion     Normal
 hi def link snipVisual           Normal
-hi def link snippet              Normal
+hi def link snipSnippet          Normal
 
 hi def link snipGlobalStart      Statement
 hi def link snipGlobalEnd        Statement
@@ -84,4 +105,6 @@ hi def link snipGlobal           Normal
 hi def link snipClear            Statement
 hi def link snipPriority         Statement
 
+" }}}1
+
 let b:current_syntax = "snippets"