title: how to add multiple formats to the same text with XlsxWriter
body: <p>The following examples from the <a href="https://github.com/jmcnamara/XlsxWriter/blob/master/dev/docs/source/worksheet.rst#worksheetwrite_rich_string" rel="nofollow noreferrer">docs</a> work great:</p>
  
  <pre><code>import xlsxwriter
  
  workbook = xlsxwriter.Workbook('rich_strings.xlsx')
  worksheet = workbook.add_worksheet()
  
  worksheet.set_column('A:A', 30)
  
  # Set up some formats to use.
  bold = workbook.add_format({'bold': True})
  italic = workbook.add_format({'italic': True})
  red = workbook.add_format({'color': 'red'})
  
  # Write some strings with multiple formats.
  worksheet.write_rich_string('A1',
                              'This is ',
                              bold, 'bold',
                              ' and this is ',
                              italic, 'italic')
  </code></pre>
  
  <p>But how would I do something <strong><em>bold and italic</em></strong>?</p>
  
  <p>The following does not work.</p>
  
  <pre><code>worksheet.write_rich_string('A1',
                              'This is ',
                              bold, 'bold',
                              ', this is ',
                              italic, 'italic',                                
                              ', and this is',
                              bold and italic, ' bold and italic')
  </code></pre>