• RT #85350; retain WS around "+" and "-" operators, so that we don't break
  the "calc()" function by accident.
  Thanks to Philipp Soehnlein
  
• RT #60239; remove WS around ">" and "~" selector combinators
  Thanks to Jacob R.
  
• RT #60238; remove units on zero values (e.g. "0px" -> "0")
  Thanks to Jacob R.
  
• RT #85896 and #79792; allow builds on Perls older than 5.8.8
  Thanks to Michael Robinton