Lets say we have the following XML structure: <pre class="prettyprint"><code><a>2<d>4</d><c>3</c></a> </code></pre> Why does <code>sum(//*)</code> return 274?

Because it's 243 + 24 + 3 + 4 = 274 <code>//*</code> means all elements, which are <code>a</code>, <code>b</code>, <code>c</code>, and <code>d</code>. Then, we summarize their text values, which include everything except tags. I think, what you're looking for is <code>sum(//*/text())</code>, which is 9 in this case