As a domain expert in web development, I can confirm that HTML is not case sensitive when it comes to tag names. This means that you can use uppercase, lowercase, or a combination of both when writing your HTML tags, and the browser will still interpret them correctly. However, it's important to note that while HTML itself is case insensitive, CSS (Cascading Style Sheets) is case sensitive, so it's a good practice to be consistent with your case usage to avoid confusion. read more >>

In documents in the HTML syntax: Tag names for HTML elements may be written with any mix of lowercase and uppercase letters that are a case-insensitive match for the names of the elements given in the HTML elements section of this document; that is, tag names are case-insensitive.read more >>