So they take a word "whitespace" which needs no hyphen and jam one in. Then they take two completely distinct words "no wrap" and jam them together with no separator. And then you have to remember both of these on the same rule.
Also, the entire semantics are a bit strange. When I'm deciding whether I want text to line wrap, I don't really think about whether the whitespace should wrap. Yes, whitespace is somewhat relevant to the topic, since that's one option of where to break lines in order to line wrap, but I still think of it as the entire text that is line wrapping.
Oh, and don't forget that there is in fact a word-wrap property, which is a much better name for the previous behavior, but in fact only customizes how the line-breaking algorithm determines which words can be broken apart.
The naming is far from great, but there is a method to the madness. Here's a talk I did a while back on how various line breaking things fit together: https://cssday.nl/2019/speakers#florian
This is at the top of the list in the Incomplete List of Mistakes in the Design of CSS[1]. Which has been discussed several times on HN (last 2 months ago)[2].
As far as I can tell, both are common, but “white space” is more common as a synonym to negative space, and “whitespace” is more common to refer to the characters. If so, the “white-space” property controls whitespace, not white space.
This just reminded me of the first bug of my career that took me hours trying to figure out. Colors weren't working correclty in IE 6 (pre IE Developer Tools) and I eventually learned that Firefox accepted both spellings "gray" and "grey", whereas IE only one of them.
Don't remember which one I used, but do remember that I went home early that day after that :/
"Sienna" is an extremely ambiguous color already. Image search for "sienna color" and you'll get a huge range of browns, reds and oranges.
"Burn sienna" seems even more varied. Here's are four different color-oriented websites, with a dark earthy orange from Colorlex [1], a light salmon from Canva [2], a light brown from Benjamin Moore [3] and a dark brown from Atelieracrylic [4].
Worth watching the Technology Connection video on the colour Brown [1]. It's a strange colour that only really exists when placed in the context of other colours, not something that can really be produced by a pure RGB light source, which explains why the CSS Brown colour looks red.