constructor({declaration, specifiers, comments}) {
    super('ExportNamedDeclaration');
    this.declaration = declaration;
    this.specifiers = specifiers;
    this.comments = comments;
  }
Constructed with either declaration or specifiers.
@param {Object} cfg
@param {Object} cfg.declaration Any *Declaration node (optional)
@param {Object[]} cfg.specifiers List of specifiers (optional)
@param {Object[]} cfg.comments Comments data (optional)