What is the critical rendering path? What stages does it include?

The critical rendering path is the sequence of steps that the browser performs to display the page content to the user. Optimizing this path helps speed up the page load and rendering times.

Main stages of the critical rendering path:

1. Loading HTML — the browser receives and parses the HTML document.
2. Building the DOM (Document Object Model) — creating the structure of page elements.
3. Loading and parsing CSS — fetching and processing CSS files to build the CSSOM (CSS Object Model).
4. Building the CSSOM — the style tree that, together with the DOM, forms the render tree.
5. Constructing the Render Tree — combining the DOM and CSSOM, considering element visibility and styles.
6. Layout (Reflow) — calculating the sizes and positions of elements on the page.
7. Painting — rendering pixels on the screen.

Optimizing the critical path involves minimizing the number and size of resources blocking rendering (such as CSS and JS), using asynchronous script loading, inlining critical CSS, and other techniques.