As an SEO professional, you need to understand what the DOM is, because it’s what Google is using to analyze and understand webpages.
The DOM is what you see when you “Inspect Element” in a browser. Simply put, you can think of the DOM as the steps the browser takes after receiving the HTML document to render the page.
The first thing the browser receives is the HTML document. After that, it will start parsing the content within this document and fetch additional resources, such as images, CSS, and JavaScript files.
The DOM is what forms from this parsing of information and resources. One can think of it as a structured, organized version of the webpage’s code.
Nowadays the DOM is often very different from the initial HTML document, due to what’s collectively called dynamic HTML. Dynamic HTML is the ability for a page to change its content depending on user input, environmental conditions (e.g. time of day), and other variables, leveraging HTML, CSS, and JavaScript.
Simple example with a <title> tag that is populated through JavaScript:
