Question 11 :
How does HTML differ from XHTML ?
XHTML has a small number of differences. The most noticeable being the requirement for elements to be lowercase (e.g. <p> and not <P>) and elements to be closed (e.g. paragraphs must end with a </p>).
Question 12 :
Why to type a tags in uppercase, and never bother closing the paragraphs ?
For reasons on internationalisation XML elements are case sensitive. A choice had to be made, and lowercase won on the day.
Tags may not overlap
This is <em> emphasized text and <b>bold </em>text</b>
This is <em>emphasized text </em> is <b>bold text</b>
Only certain tags may nest inside other tags
Looking at the dtd for xhtml, the definition of the "ol" element is:
<!ELEMENT ol (li)+> <!ATTLIST ol %attrs; type %OLStyle; #IMPLIED compact (compact) #IMPLIED start %Number; #IMPLIED > This implies that an order list, "ol", element may not contain paragraph tags or body text, just list items. <ol>
These are some of my favorite animals:
<li>octopus</li> <li>shrew</li> <li>lemur</li> and my most favorite <li>meerkats</li> </ol>
<p>These are some of my favorite animals:</p> <ol> <li>octopus</li> <li>shrew</li> <li>lemur</li> <li>meerkats</li> </ol>