The HTML string is different from the traditional selectors in that it creates the DOM elements representing that HTML string, on the fly, to be (assumedly) inserted into the document later.
You can learn stuff from experts like HTML, Photography or even how to animate your own YouTube videos from the largest YouTube channel in Germany — Kurzgesagt.
If you're just starting out in this, there's one called, 'Hand Coding Your First Website' by a guy named Rich Armstrong, which goes in depth on the basics of HTML and CSS.
如果你刚刚开始做这个,有一个叫做“手工编码你第一个网站”人叫 Rich Armstrong,深入讲解 HTML 和 CSS 基础知识。