code: function File(filepath, data, importer) {
    this.file = filepath;
    this.data = data;
    this.importer = importer;
    this.includedFiles = [];
    this._cb = [];
    _.cacheFile(filepath);
  }
docs: File
  Handler for parsing loaded file data into an AST.
  Parsing resolves import statements, thus may request additional files.