Whereas some text search engines require users to enter two or three words separated by white space, other search engines may enable users to specify entire documents, pictures, sounds, and various forms of natural language.
而一些文本搜索引擎要求用户输入由白色空格分隔的两个或三个字，其他搜索引擎可以使用户能够指定整个文档，图片，声音和各种形式的自然语言。