What does the <DOCTYPE> declaration do in an HTML document?

The declaration serves as a way to inform the web browser about the version of HTML that the document is written in. This declaration is placed at the very beginning of an HTML document and is crucial because it helps the browser render the page correctly. By specifying the version, the browser can understand the rules and features that should be supported when processing the HTML code.

In HTML5, for example, the declaration is simply “,” indicating to the browser that the document is an HTML5 document. If a different version of HTML were being used, such as HTML 4.01, the declaration would be different and more complex. Correctly specifying the version through the is vital, as it ensures that the document will be displayed as intended and that all elements of the HTML are treated appropriately according to that specification.