In this chapter, we learned how web pages are written in HTML and stylized by CSS. CSS selectors can be used to match HTML nodes so that their contents can be extracted. Well-written HTML documents can also be queried by XPath Expression, which has more features and is more flexible. Then we learned how to use the element inspector in modern web browsers to figure out a restrictive selector to match the HTML nodes of interest so that the needed data can be extracted from web pages.
In this next chapter, we will learn a series of techniques that boost your productivity, from R Markdown documents, diagrams, to interactive shiny apps. These tools make it much easier to create quality, reproducible, and interactive documents, which are very nice ways to present data, ideas, and prototypes.