we have a more modern implementation in the next beta
I tested the following with various flavors: $ x\mathstrut_{3} x_{3} x^3 x\mathstrut^3 x^\circ x\mathstrut^\circ 20\mathstrut^\circ 20^\circ $ Flavors that I tried: 2014.03.27 MkIV 2014.02.14 MkIV 2013.06.07 MkII (from latest beta) pdfTeX 1.40.14 (from Debian TL 2013) (wrapping in \(start|stop)text or ending with \bye, as appropriate). My observations: The MkII and pdftex subscripts look too high. I know that's sacreligious, since it is what Knuth must have intended, and I am surprised that I didn't notice it before. The 2014.02.14 MkIV subscript with the strut looks too low, although the x^3 with the strut looks reasonable, or is maybe just slightly too high. The x^\circ looks fine. The x\mathstrut^\circ is too high. But the 20\mathstrut^\circ looks right (and looks too low without the strut). In 2014.03.27 MkIV, the subscript- and subscript heights are unchanged by the strut. The subscript heights look right. The superscript heights all look okay, except for the 20\mathstrut^\circ, which is too low (same height as without the strut). In earlier versions, one could raise the \circ using a \mathstrut, but that no longer has an effect. The other change, and maybe I am hallucinating this one, is that the horizontal spacing between the x and the 3 is now slightly different with and without the strut: It is tighter with the strut. I think it looks better without the strut, but am not sure. So, overall I think it has improved. I also wonder: 1. about the right horizontal spacing (how tight it should be) 2. how to raise the \circ in 20^\circ -Sanjoy