What is the purpose of the DOCTYPE declaration in HTML?

The DOCTYPE declaration serves a crucial role in web development by specifying the HTML version that a document adheres to. This declaration appears at the very top of an HTML document and signals to the browser which set of rules (or standards) to use when rendering the page. When the correct DOCTYPE is declared, it helps ensure that browsers interpret the HTML correctly and display the content as intended.

For example, using the correct DOCTYPE for HTML5 () tells the browser to render in standards mode, which aligns with newer HTML features and standards. This prevents the browser from using quirks mode, which could lead to inconsistent behavior and display issues across different browsers. Therefore, the purpose of the DOCTYPE declaration is fundamentally about compliance with a specific version of HTML, ensuring consistent rendering behaviors across various web environments.