title: OpenXML escaping illegal characters
body: <p>I am doing some string replacement within a Word Docx file using <a href="https://powertools.codeplex.com/" rel="noreferrer">OpenXML Power Tools</a> and it is working as expected. However things break when I have invalid characters in the substitution such as <strong>ampersand</strong>, so for instance "Harry &amp; Sally" will break and produce an invalid document. According to <a href="https://stackoverflow.com/questions/5875322/ooxml-sdk-illegal-character-replacements">this post</a> illegal characters need to be converted to xHHHH.</p>
  
  <p>I am having trouble finding the contents to the OOXML clause mentioned in the post and hence escaping characters appropriately. </p>
  
  <p>I am hoping someone either has some code or insights into exactly what characters need to be escaped. I was also hopeful OpenXML Power Tools could do this for me in some way, but I cannot seem to find anything in there either. </p>