When comparing the "superiors" feature with the "fractions" feature in a number of OpenType fonts from Adobe and Linotype (and others?), some questions arise. Specifically, in the superior glyph range, why do letters have a different baseline from numbers and punctation? This is not the case with glyphs covered by the fractions feature.
Here are some examples illustrated:
Superior numbers have a higher baseline than superior letters. Why? (Illustrated above: [normal capital H], [superior 1], [superior 2], [superior 2], [superior 3], [superior a], [superior b], [normal lowercase c])
What this leads to, is impossible typography, as pictured above. The period should have the same baseline as the superior letter, no? Instead, it has the baseline of the numbers.
Fraction numbers are larger than superior numbers. This is understandable.
Fraction numbers and letters share a common baseline. This seems to make typographic sense. Why here and not with superiors?
Could this have something to do with a legacy work-around? If a type designer, or major type foundry, were to change this, would it cause any problems? Are there users who expect the superior feature to be defined in this manner?