There's a variable

$default_sort_order = '[

"position",

"top",

"right",

"bottom",

"left",

"z-index",

"display",

"visibility",

"-webkit-flex-direction",

"-moz-flex-direction",

"-ms-flex-direction",

"-o-flex-direction" [...]

defined in https://github.com/csscomb/csscomb-for-vim/blob/master/plugi..., so I guess that's what CSSComb uses, although it says one can define custom orderings.

I guess it's useful if you write lots of CSS and don't want to bother with thinking about the ordering at code-time?