Question

How do browsers understand HTML?

What is the actual processing that takes place internally so that the browser renders HTML in the proper viewable way?

Answer 1

It depends on the particular browser, but the general procedure goes something like this:

1. Read the HTML and parse it into a DOM tree.
2. Load linked resources (stylesheets, scripts, images, media)
3. Calculate the page layout (positions, sizes, colors, fonts, etc.)
4. Render the page

In modern browsers, these operations run partly in parallel, making things much more complicated than they seem.

If you want to know more details, you could look at the source code – at least Firefox (and other Gecko-based browsers) and WebKit (the basis of Google Chrome and Safari) are Open Source.