Points in CSS specificity

Question

Researching specificity I stumbled upon this blog - http://www.htmldog.com/guides/cssadvanced/specificity/

It states that specificity is a point-scoring system for CSS. It tells us that elements are worth 1 point, classes are worth 10 points and IDs are worth 100 points. It also goes on top say that these points are totaled and the overall amount is that selector's specificity.

For example:

body = 1 point
body .wrapper = 11 points
body .wrapper #container = 111 points

So, using these points surely the following CSS and HTML will result in the text being blue:

CSS:

#a {
    color: red;
}

.a .b .c .d .e .f .g .h .i .j .k .l .m .n .o {
  color: blue;
}

HTML:

<div class="a">
  <div class="b">
    <div class="c">
      <div class="d">
        <div class="e">
          <div class="f">
            <div class="g">
              <div class="h">
                <div class="i">
                  <div class="j">
                    <div class="k">
                      <div class="l">
                        <div class="m">
                          <div class="n">
                            <div class="o" id="a">
                              This should be blue.
                            </div>
                          </div>
                        </div>
                      </div>
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</div>

RESULT:

http://jsfiddle.net/hkqCF/

Why is the text red when 15 classes would equal 150 points compared to 1 ID which equals 100 points?

EDIT:

So apparently the points aren’t just totalled, they’re concatenated. Read more about that here - http://www.stuffandnonsense.co.uk/archives/css_specificity_wars.html BUT, does that mean that the classes in our selector = 0,0,15,0 OR0,1,5,0?

My instincts tell me it’s the former as we KNOW the ID selector’s specificity looks like this: 0,1,0,0

Answer 1

The current Selectors Level 4 Working Draft does a good job of describing Specificity in CSS:

Specificities are compared by comparing the three components in order: the specificity with a larger A value is more specific; if the two A values are tied, then the specificity with a larger B value is more specific; if the two B values are also tied, then the specificity with a larger c value is more specific; if all the values are tied, the two specifities are equal.

This means that the values A, B and C are completely independent of each other.

15 classes doesn't give your selector a specificity score of 150, it gives it a B value of 15. A single A value is enough to overpower this.

As a metaphor, imagine a family of 1 grand parent, 1 parent and 1 child. This could be represented as 1,1,1. If the parent has 15 children, that doesn't suddenly make them another parent (1,2,0). It means that the parent has an awful lot more responsibility than they had with just 1 child (1,1,15). ;)

The same documentation also goes on to say:

Due to storage limitations, implementations may have limitations on the size of A, B, or c. If so, values higher than the limit must be clamped to that limit, and not overflow.

This has been added to tackle the problem presented in Faust's answer, whereby CSS implementations back in 2012 allowed specificity values to overflow into each other.

Back in 2012, most browsers implemented a limitation of 255, but this limitation was allowed to overflow. 255 classes had an A,B,c specificity score of 0,255,0, but 256 classes overflowed and had an A,B,c score of 1,0,0. Suddenly our B value became our A value. The Selectors Level 4 documentation completely irradiates that problem by stating that the limit can never be allowed to overflow. With this implementation, both 255 and 256 classes would have the same A,B,c score of 0,255,0.

The problem given in Faust's answer has since been fixed in most modern browsers.