title: Case conventions on element names?
body: <p>Are there any <em>formal</em> recommendations on element casing in XML?</p>
  
  <p>I know XHTML uses lowercase element names (as opposed to HTML which canonically uses uppercase but is case-insensitive.)</p>
  
  <p>But I'm talking about XML for generic content.</p>
  
  <h2>lowercase:</h2>
  
  <pre><code>&lt;customer&gt; 
     &lt;accountnumber&gt;619&lt;/accountnumber&gt;
     &lt;name&gt;Shelby Lake&lt;/name&gt;
  &lt;/customer&gt;
  </code></pre>
  
  <h2>camelCase:</h2>
  
  <pre><code>&lt;customer&gt; 
     &lt;accountNumber&gt;619&lt;/accountNumber&gt;
     &lt;name&gt;Shelby Lake&lt;/name&gt;
  &lt;/customer&gt;
  </code></pre>
  
  <h2>PascalCase:</h2>
  
  <pre><code>&lt;Customer&gt; 
     &lt;AccountNumber&gt;619&lt;/AccountNumber&gt;
     &lt;Name&gt;Shelby Lake&lt;/Name&gt;
  &lt;/Customer&gt;
  </code></pre>
  
  <h2>UPPERCASE:</h2>
  
  <pre><code>&lt;CUSTOMER&gt; 
     &lt;ACCOUNTNUMBER&gt;619&lt;/ACCOUNTNUMBER&gt;
     &lt;NAME&gt;Shelby Lake&lt;/NAME&gt;
  &lt;/CUSTOMER&gt;
  </code></pre>
  
  <p><strong>Note:</strong> I'm looking for cited guidelines rather than opinions. But the opinion with the most up-votes can be considered a guideline.</p>