Attribute names when calling face-attribute

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I am implementing ricci calculus notation.

Regarding the face-attribute function.  Is the attribute pre-defined or can
I select the attribute name?

For instance, could I call "(face-attribute 'default :size)" rather than
"(face-attribute 'default :height)"?
Here is my function

(defun ricci-size (size)
  "Return integer SIZE of superior and inferior glyph.
SIZE  typeface height. Integer scaled in 1/10 of point size.
Not smaller than value set by `ricci-minsize'."

  (ceiling
     (max
        (if (integerp ricci-minsize)
        ricci-minsize
      (condition-case nil ; For bootstrapping.
          (* ricci-minsize
         (face-attribute 'default :height))
        (error 0)))
    (* height ricci-scale))))  ; assumes height is integer.