Accessibility is the practice of ensuring that websites, web applications, documents, and digital content are available and usable by individuals of all abilities and disabilities. It aims to provide equal access and equal opportunity to everyone, regardless of their physical or cognitive limitations.

HTML markup formatting can be used to enhance accessibility by adding subtitles or captions to make content more comprehensible to users. This can be achieved using the following HTML tags and attributes:

1. `

` – This tag is used to define a heading that provides a clear and concise title for a section of content.
2. `

` – Represents a paragraph, which is a block of text that can contain multiple sentences or lines.
3. `` – This tag highlights important or emphasized text within a paragraph.
4. `` – This tag emphasizes or gives emphasis to certain parts of the text.
5. `

` – Represents an unordered list, typically used for displaying a list of items without a specific order.
6. `
• ` – Defines an individual list item within an unordered list.
  7. `

  ` – Indicates a section that contains quoted content from another source.
  8. `` – Creates a hyperlink, allowing users to navigate to another webpage, document, or section within the same page.
  9. `` – Defines an image and provides alternative text via the `alt` attribute, which is crucial for individuals who cannot see or have difficulty seeing images.

  Using these HTML tags and attributes, web developers can improve accessibility by structuring content in a logical manner, adding necessary descriptions for images, and providing subtitles or captions for multimedia elements to facilitate understanding and usability for individuals with disabilities.