Your understanding is incorrect. Ordinals is meant to be applied only to selected text.
Thanks Peter for your quick response. I couldn't find that in Adobe's online manuals (if you can point me to a link, it would be helpful).
So, in my paragraph, if I have an instance of "3rd" and want OpenType ordinals applied to "rd" (instead of scaled superscripts), I select "rd" only and turn on Ordinals in the character panel?
I'm pretty sure you'll find that info in the OpenType User's Guide: www.adobe.com/de/type/browser/pdfs/OTGuide.pdf
You could det it up as a GREP style pretty easily, I think.
Thanks. I scanned through the document and found this warning note (there were also mentions of how to apply ordinals in InDesign);
Like fractions, the ordinal feature should not be
applied globally, but only where needed. Some fonts may
use contextual rules to implement ordinals, while others
will turn them on for all selected text. Also, ordinals
work best with lining figures, rather than oldstyle figures,
because of the constant vertical position of the ordinals.