What is the purpose of the <iframe> tag?

The purpose of the <iframe> tag is to create an inline frame within a page. This allows you to embed another HTML document within the current page, effectively allowing for the inclusion of external content such as videos, maps, or other web pages without restructuring the entire layout of your page.

Using the <iframe> tag, the specified source can be displayed while keeping the surrounding content intact and separate. This is particularly useful for integrating content from different sources while maintaining a cohesive user experience.

Other options don't match the functionality of the <iframe>. For instance, creating a full-width frame or defining a frame set pertains to older HTML structures that involve framesets, which are not commonly used in modern web design. Additionally, using an iframe does not serve the purpose of holding content specifically for unsupported browsers; instead, it serves as a way to present multiple sources of content seamlessly within the same page frame.