<human>:  What is the difference between HTML and XHTML?
<bot>: The main difference between HTML and XHTML is that XHTML is an XML-based version of HTML, which adheres more strictly to the XML syntax and rules. HTML is HTML, which can have more flexibility in its syntax. XHTML documents must be well-formed, meaning that elements must be properly nested and closed, and must only use lowercase tags. HTML documents do not have this restriction, so an HTML document can contain a mix of uppercase and lowercase tags. Additionally, XHTML requires that certain attributes be included in the tags, such as including a type attribute in the <script> tag or including the attribute 'alt' in the <img> tag. HTML does not have this requirement.