title: When is an EM space not an EM space? (U+2003, HTML)
body: <p>So I'm given some text that was formatted using EM space, EN space, and the various other Unicode fixed-size white space characters, and it works fine in Firefox, Chrome, and Edge (latest versions) on English Windows 10 64-bit.  I use the following CSS to make it display properly.</p>
  
  <pre><code>white-space: pre
  </code></pre>
  
  <p>However, I got a complaint that things weren't properly aligned from a user in Taiwan. I suggested trying a different browser. He started with Edge, moved to Chrome (same problem), and then to Firefox (same problem). Remotely debugging on his his computer (and using Firefox debugger which I am most familiar with), I finally determined that EM space on his computer (Chinese Windows 10, 64-bit) width was calculated the same as EN space, or half the size it should be. This was the source of the misalignment. As a workaround, in the debugger, I replaced a number of the EM spaces with pairs of EN spaces, and this produced the correct alignment.</p>
  
  <p>Since the symptom was the same in 3 different browsers, it seems likely to be a Windows issue... but why would an EM space be treated differently in different language versions of Windows? I know that normal space U+0020 can vary in width based on font, but no normal spaces are used in this body of text for alignment purposes.</p>
  
  <p>I verified that the identical web-hosted font was being used on both machines, and using fonttools verified that the width for U+2003 is 1000 and for U+2002 is 500 (design units).</p>
  
  <p>What good is the Unicode EM space if it is sized differently on different machines?
  Are there other characters that are also sized differently?</p>
  
  <p>While I have a workaround that I could apply using search and replace when I get updates to this body of text, that would work for this user, how robust is the workaround to other language-versions of Windows (if that is the source of the problem)?</p>
  
  <p>Are there other similar workarounds necessary for other language-versions for other characters with well-defined sizes?</p>
  
  <p>The layout also works on English versions of Android that I have on hand, but I have no Linux, Mac, or non-English Android or Windows to test with, generally.</p>