def numeric_specificity(tag_name, nesting_parts)
        nesting_parts = nesting_parts.dup
        name_parts = tag_name.split(':')
        specificity = 0
        value = 1
        if nesting_parts.last == name_parts.last
          while nesting_parts.size > 0
            if nesting_parts.last == name_parts.last
              specificity += value
              name_parts.pop
            end
            nesting_parts.pop
            value *= 0.1
          end
          specificity = 0 if (name_parts.size > 0)
        end
        specificity
      end
def numeric_specificity(tag_name, nesting_parts)
        nesting_parts = nesting_parts.dup
        name_parts = tag_name.split(':')
        specificity = 0
        value = 1
        if nesting_parts.last == name_parts.last
          while nesting_parts.size > 0
            if nesting_parts.last == name_parts.last
              specificity += value
              name_parts.pop
            end
            nesting_parts.pop
            value *= 0.1
          end
          specificity = 0 if (name_parts.size > 0)
        end
        specificity
      end
Returns the specificity for +tag_name+ at nesting defined
 by +nesting_parts+ as a number.