Rules That Browsers Must Follow

10 Feb 2026

Google Chrome dominates more than 65% of the commercial browser market, and Chromium—the engine behind Chrome—is also used by other major browsers such as Microsoft Edge. Because of this, understanding how Chrome works is effectively the same as understanding how web services are delivered to roughly 70–80% of all browser users.

That said, the browser ecosystem as a whole is enormous. Even a browser with just a 1% market share can still represent tens of millions of users worldwide. For this reason, understanding Chrome’s internals does not automatically mean understanding how all browsers work. Rather, it helps us understand how Chromium-based browsers behave.

Fortunately, Chrome is not built on proprietary rules unique to itself. To function as a web browser, it must follow a set of shared standards: how network communication works, how HTML is parsed, and in what order content is rendered on the screen. These rules are defined as standardized interfaces that all modern browsers are expected to implement.

These standards are defined and maintained by international web standards organizations such as W3C, WHATWG, and ECMA International. Modern web services are built in accordance with these specifications, and browsers are implemented to comply with them. Collectively, these specifications are often referred to as web standard interfaces.

Although we may examine browser behavior through Chrome, its implementation is based on these shared standards. As a result, we can reasonably expect browsers like Firefox or Safari to behave in similar ways, even if their internal implementations differ.

So, which organizations define these interfaces? Among several groups, W3C and WHATWG play the most prominent roles. In addition, IETF and ECMA International are responsible for specifications related to networking and JavaScript.

The World Wide Web Consortium (W3C) was founded in 1994 by Tim Berners-Lee, widely recognized as the inventor of the World Wide Web. As the web rapidly expanded into commercial use, the need for standardization became clear, leading to the formation of W3C.

W3C has been responsible for developing and maintaining many foundational web standards, including HTML, XML, CSS, SVG, and web accessibility guidelines. While the living standards for HTML and DOM are now managed by WHATWG, CSS specifications are still maintained by W3C.

Browsers are implemented to comply with CSS standards defined by W3C. For example, when W3C specifies how a child selector should work, browsers interpret CSS written with that selector accordingly and apply styles based on those rules.

The Web Hypertext Application Technology Working Group (WHATWG) was formed in 2004 by browser vendors such as Mozilla, Apple, and Opera. At the time, they believed W3C was not evolving fast enough to meet the practical needs of modern web applications.

WHATWG maintains living standards for core web technologies such as HTML, DOM, and the Fetch API. These specifications are continuously updated online and define how modern browsers—including Chrome—should behave. In addition to HTML and DOM, WHATWG manages standards for storage, streams, console APIs, WebSockets, URLs, and other essential web platform features.

For example, WHATWG defines how HTML tags are identified and parsed. When a browser receives an HTML document from a web server and begins parsing it, it follows these rules. If it encounters a string like <div>, it recognizes the angle brackets as delimiters and identifies div as a semantic HTML element, then processes it accordingly.