What primary attribute does the doctype declaration influence?

The doctype declaration primarily influences the validation of HTML code. It specifies which version of HTML the document is using, helping browsers to render the page correctly according to the rules of that version. By declaring a doctype, developers ensure that their code adheres to standards set for that particular version of HTML, facilitating proper functionality and compatibility across different web browsers. This is crucial for maintaining consistency in how web content is displayed and interacted with.

While the layout of the web page can be affected by how browsers interpret the code, it is the doctype that serves as a foundational element for validation. This validation process is essential for developers aiming to create high-quality, standards-compliant web pages. Security measures and loading speed are influenced by other factors, such as server configuration and code optimization, rather than the doctype itself.