What are "proprietary" tags?

Proprietary tags refer to tags that are specifically designed to work only on particular browsers or platforms, often due to the unique features or capabilities that those browsers offer. These tags are typically not standardized and may not render or function correctly in all web environments, leading to inconsistencies in how content is displayed or interacted with by users on different browsers.

In the context of web development, using proprietary tags can limit the compatibility of a website or web application, as it may not be accessible or functional for users on other browsers or devices. This is why it's essential for web developers to focus on using standard HTML and CSS tags to ensure a more uniform experience across all platforms.

The other options present different concepts that are not related to the idea of proprietary tags. While ownership of content and copyright information are important in the realm of web development, they do not define what proprietary tags are.