<!DOCTYPEhtml><htmllang="en"><head><metacharset="UTF-8"><metahttp-equiv="X-UA-Compatible"content="IE=edge"><metaname="viewport"content="width=device-width, initial-scale=1.0"><title>Document</title></head><body>
Hello World! My First Webpage!
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1. 文档类型说明
<!DOCTYPEhtml>
DTD(Document Type Definition,文档类型说明)
<!DOCTYPE>声明位于文档中最前面的位置,处于html标签之前,此标签可告知浏览器使用哪种 HTML 或 XHTML 规范