
To show the different size fonts.
You will see the changed font values.
Right below the top value of the tree are the substitution values section for each font.

Rather then have three sets of properties for each font type, we have substitution values for each size.
For example, take $ScrollBarWidth$.
Blue\Values\General\Sysmetrics :

The $$'s show that the value is located under Blue\Normal\Substitution, Blue\LargeFonts\Substitution, and Blue\ExtraLarge\Substitution
Blue\Normal\Substitution

Blue\LargeFonts\Substitution

When Normal Fonts is used, the scrollbar width will be 17.
When Large Fonts is used, the scrollbar width will be 19.