code: function processSync(doc) {
      var complete = false
      var file
  
      freeze()
      assertParser('processSync', processor.Parser)
      assertCompiler('processSync', processor.Compiler)
      file = vfile(doc)
  
      process(file, done)
  
      assertDone('processSync', 'process', complete)
  
      return file
  
      function done(err) {
        complete = true
        bail(err)
      }
    }
docs: Process the given document (in string or vfile representation), sync.