title: Looking for a clear description of Excel's .xlsx XML format
body: <p>Microsoft Excel's ".xlsx" files are zip files that each contain a set of files. </p>
  
  <p>Could someone please provide a link that concisely describes the full structure/syntax/markup/format of the embedded <code>.xml</code> files (the headers are less interesting)?</p>
  
  <p>For example, it's hard to find online explanations on what the <code>c</code>, <code>t</code>, and <code>s</code> elements represent.</p>