How does Scrapy (Open Source Web Scraping Framework) works?

Quoting from Scrapy Official Documentation :

Scrapy comes with its own mechanism for extracting data. They’re called selectors because they “select” certain parts of the HTML document specified either by XPath or CSS expressions. Source

After reading this, I'm still not sure whether Scrapy works by directly selecting parts of the HTML document by using XPath/CSS expressions or selecting nodes from DOM Tree which is rendered by the browser?

Still confused whether DOM Parsing and HTML Parsing is the same or not...