title: The separator between keywords in PDF meta data
body: <p>I cannot find an "official" documentation on whether the keywords and keyword phrases in the meta data of a PDF file are to be separated by a comma or by a comma with space.</p>
  
  <p>The following example demonstrates the difference:</p>
  
  <ul>
  <li>keyword,keyword phrase,another keyword phrase</li>
  <li>keyword, keyword phrase, another keyword phrase</li>
  </ul>
  
  <p>Any high-quality references?</p>
  
  <p>The online sources I found are of low quality.
  E.g., an <a href="http://www.adobepress.com/articles/article.asp?p=1998556&amp;seqNum=7" rel="noreferrer">Adobe press web page</a> says "keywords must be separated by commas or semicolons", but in the example we see a semicolon with a following space before the first keyword and a semicolon with a following space between each two neighbor keywords. We don't see keyword phrases in the example.</p>