crawl complete website with DOM Document in PHP given by user [duplicate]

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• How to web crawl some sites [closed] 1 answer

I am making a web scrapper , I can get the sub urls from user given url and load the content from sub pages. I am using getElementsByTagName('body');in domdocument . but how can i get specific data from class. I can not know its classes when the crawler input would be to user. so How can I scrap any website properly that user gives as input?/ i am getting body contents ,I need to show the contents properly . any help?