code: function parse(doc) {
      var file = vfile(doc)
      var Parser
  
      freeze()
      Parser = processor.Parser
      assertParser('parse', Parser)
  
      if (newable(Parser)) {
        return new Parser(String(file), file).parse()
      }
  
      return Parser(String(file), file) // eslint-disable-line new-cap
    }
docs: Parse a file (in string or vfile representation) into a unist node using the `Parser` on the processor.