css3-values says

  # keyword values (such as ‘auto’, ‘disc’, etc.), which appear literally,
  # without quotes (e.g. auto)

so for the value definition of each property table, the keywords shouldn't be quoted.

This also applies to some of the data type definitions, such as

  # <track-minmax>  => 'minmax(' <track-breadth> ',' <track-breadth> ')' 
  #| 'auto' | <track-breadth> 

see [1] for a similar example in css3-iamges.

I am not sure how to deal with '[', perhaps someone raise that as a question on www-style.

[1] http://dev.w3.org/csswg/css3-images/#image-list-type