But the meaning does change based on the parent tag. <p> is not allowed to be nested, just like <li> and many other elements. Those are rules anyone writing markup has to remember, whether XML or not. Allowing <li> to close the previous <li> is a natural extension of that rule, and strikes a good balance between the rigor of XML and brevity of Markdown, whose context rules I find to be both less consistent and incredibly difficult to remember. (Can a list contain a list? Does ^ superscript a whole line or just a word? What elements can contain a table?)