How do I turn on Microsoft's Oxford (serial) comma checker?

Microsoft Editor has some of the best checking for Oxford commas available today. At time of writing, it only works on lists of four or more items, but aside from that, we think it's better than PerfectIt's own checker. So if you want to enforce Oxford commas, you can turn on Microsoft Editor's checking with these instructions for Windows and for Mac:

Windows

• Open Word and click "File".
• Click "Options".
• Click "Proofing". If you would like Word to mark grammar issues in the document, make sure the option for "Mark grammar errors as you type" is ticked.
• Next to Grammar and Refinements, click "Settings".
  
• Under "Punctuation Conventions" tick the box for Oxford Comma.
  
  

If you have set Word to mark up grammar errors as you type, issues in the document will appear with a blue dotted line under the word:

You can run the Spelling and Grammar check by clicking the Editor button under "Review" in the ribbon:

Oxford comma results are listed under "Punctuation Conventions" in the Editor pane:

 

Mac

• Open Word and click the "Word" menu item. Click "Preferences".
  
  
• Click "Spelling & Grammar".
  
  
• The setting for Oxford Comma is near the bottom of the list - scroll down and check the box, then click "OK". Close the Preferences window.
  
  

If you have set Word to mark up grammar errors as you type, issues in the document will appear with a blue dotted line under the word:

You can run the Spelling and Grammar check by clicking the Editor button under "Home" in the ribbon:

Oxford comma results are listed under "Punctuation Conventions" in the Editor pane: