constructor(ast, pathResolver) {
    this._ast = ast;
    this._pathResolver = pathResolver;
    this._results = [];
    this._processedClassNodes = [];

    this._inspectExportDefaultDeclaration();
    this._inspectExportNamedDeclaration();

    // file doc
    const doc = new FileDoc(ast, ast, pathResolver, []);
    this._results.push(doc.value);

    // ast does not child, so only comment.
    if (ast.program.body.length === 0 && ast.program.innerComments) {
      const results = this._traverseComments(ast, null, ast.program.innerComments);
      this._results.push(...results);
    }
  }
create instance.
@param {AST} ast - AST of source code.
@param {PathResolver} pathResolver - path resolver of source code.