Why csscss doesn't remove duplication for you
After I released csscss, I've been asked numerous times:
Why doesn't csscss remove duplication for me?
That is a fair question. It is easy to look at csscss and ask why it isn't more like a minifier that a developer can just run before deploying updates. In fact CSSO and css-ractionator are projects that do this exact thing.
So why didn't I build it that way?
csscss forces me consider my (code) design
I built csscss as a tool to help a developer write smarter CSS. Duplication isn't all bad, but we often write duplicated CSS unknowingly. When I see duplicated CSS, it forces me to think about my rules and structure. It forces me to ask myself several questions about my code.
"Is this necessary?"
"Have I already defined a structure for this? Do I need to extend existing structures?"
"Is there a better way to define the same rules?"
"Can I leverage other CSS tools to better structure these styles? (Sass, LESS, etc)"
All of these answers reduce duplication, but more importantly, they force me to consider the design of my code. And I don't think there is a single algorithm that satisfies all cases.
Now you can obviously do this without an automated tool. And it is easy for a small number of rules. However as your site/application grows it is extremely difficult to continue this mental juggling.
I like to think of csscss as a tool that helps extend my intuition, not replace it.
Generated code is harder to debug
If csscss generated new duplication-free code, all I am doing is punting work for later. Which usually comes up when I need to debug my styles from the browser. If the generated output is substantially different than the original source, it makes my job harder to fix my problems.
However the point of csscss is not to optimize code, it is to help inform you about areas improvement. If csscss did this for you, I expect the gulf between original source and browser CSS to be rather large.
Improving the CSS landscape
None of this is a knock against other developers working on the same problem. In fact, I think different perspectives and trial/error in this field can only be a good thing. CSS has been around for over a decade and it is surprising to me that we don't have more tools. So I commend anyone spending time to contribute. csscss is my contribution based on my opinions.
Here are some others tools that people have mentioned since I released csscss.