We extract metadata from the content of HTML metadata elements. The content of the <title> element is used for the document title, and the <meta> element can be used to specify author, subject, keywords, date, and generator application:
<head>
<title>On 7 Languages</title>
<meta name="author" content="Jasper Lutz"/>
<meta name="subject" content="An exploration of 7 programming languages"/>
<meta name="keywords" content="ruby, python, javascript, go, clojure, haskell, objective-c "/>
<meta name="date" content="2017-08-23"/>
<meta name="generator" content="DocRaptor.com"/>
</head>