support for prefixing with a highlight group.

autoload/airline/section.vim

@@ -3,17 +3,23 @@
 
 function! s:get_val(key, append)
   let part = airline#parts#get(a:key)
+
+  let val = ''
+  if exists('part.highlight')
+    let val .= '%#'.(part.highlight).'#'
+  endif
+
   if exists('part.function')
     let func = (part.function).'()'
   elseif exists('part.text')
     let func = '"'.(part.text).'"'
   elseif exists('part.raw')
-    return part.raw
+    return val.(part.raw)
   else
     return a:key
   endif
 
-  let val = ''
+
   if a:append > 0
     let val .= '%{airline#util#append('.func.')}'
   elseif a:append < 0

t/section.vim

@@ -8,6 +8,10 @@ describe 'section'
     call airline#parts#define_text('text', 'text')
     call airline#parts#define_raw('raw', 'raw')
     call airline#parts#define_function('func', 'SectionSpec')
+    call airline#parts#define('hi', {
+          \ 'raw': 'hello',
+          \ 'highlight': 'hlgroup',
+          \ })
   end
 
   it 'should create sections with no separators'
@@ -24,5 +28,10 @@ describe 'section'
     let s = airline#section#create_right(['text', 'text'])
     Expect s == '%{airline#util#prepend("text")}%{"text"}'
   end
+
+  it 'should prefix with highlight group if provided'
+    let s = airline#section#create(['hi'])
+    Expect s == '%#hlgroup#hello'
+  end
 end