How to make `hg diff` show whitespace changes?

[Noemi]

When I run `hg status`, it shows a few files as changed, but `hg diff` 
outputs absolutely nothing.  Why might this happen other than whitespace 
changes?  If it is whitespace changes, how can I make `hg diff` display 
them?  The docs explain how to ignore whitespace changes, but not how to 
make sure they're displayed.

If it makes a difference, I'm using Mercurial 3.6.3 installed using pip in 
Python 2.7.11 on Mac OS X 10.11.

Thanks!
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