While all options improve accessibility, using semantic HTML is foundational. Screen readers rely on these elements to navigate and interpret page structure (e.g., identifying navigation, main content, headers). This provides context and meaning programmatically, making the site fundamentally more accessible before other enhancements are added.

The primary issue with splash pages is user experience (UX). Most users visit a site for specific content or functionality; a splash page delays that access, often leading to frustration and increased bounce rates. While some older technologies are obsolete, the core UX principle is the strongest, universal argument against them.

The `mailto:` protocol link instructs the browser to open the user’s locally configured default email application (e.g., Outlook, Apple Mail, Thunderbird). It pre-populates the ‘To’, ‘Subject’, and ‘Body’ fields as specified in the href attribute. The behavior is dependent on the user’s OS and settings, not a web-based service.

A site map is a planning tool in information architecture. It focuses on content organization, showing the hierarchy (parent/child relationships) of pages and how they are grouped. This logical structure guides navigation design, URL schemes, and ensures users can find information intuitively, which is separate from visual design or technical implementation details.

The `` element, used with `srcset` and `sizes` attributes, allows the browser to select the most appropriate image source from a set of options based on the user’s viewport size and device resolution (pixel density). This ensures a mobile user doesn’t download a desktop-sized image, directly solving the problem of sending unnecessarily large files.

A style guide (or design system) provides standardized rules for visual design and UI components. It ensures consistency across all pages and among different developers by defining elements like color palettes, typography, spacing, and interactive component states, which is crucial for maintaining a cohesive brand and user experience.

Defense-in-depth is key for validation. Client-side validation (HTML5 `required`, JavaScript) provides immediate user feedback and improves UX. However, it can be bypassed. Server-side validation is essential for security and data integrity, as it checks the data on the server where business logic is enforced. Both layers are necessary for a robust solution.

The World Wide Web (WWW) is an information system built *on top* of the Internet. The Internet is the global network of connected computers. The Web is a specific service that uses HTTP/HTTPS protocols and hyperlinks to connect documents (web pages) and other resources. They are related but distinct concepts.