As noted in the previous post Keyboard Entry of Subscripts and Superscripts, the preferred way to enter subscripts and superscripts is by using the keyboard, rather than the math ribbon. For example, type alt+= to insert a math zone followed by a^2+b^2=c^2<space> to enter the Pythagorean Theorem. This method is a lot faster than clicking on the superscript template in the Script dropdown on the math ribbon and then filling in the desired superscript bases and superscripts. But if you don’t know about the linear format, at least you’re likely to discover the math ribbon approach, so it is useful. Interestingly enough, for PowerPoint 2010, OneNote 2010, and Excel 2010, the math ribbon structure images are all created by RichEdit from the corresponding linear format expressions. To see the latter, insert a math structure and click on the Linear option (on the math ribbon, context menu or Word’s math zone box dropdown). This will convert the built-up (Professional) form to the built-down (Linear) form.
You may want to have a base with both a subscript and a superscript. You can type it as, for example, a_j^n, which is a sub j to the nth power. You can also use the subsup template in the math ribbon Script dropdown. When you enter the subscript or the superscript, the dotted box for that “empty” script argument is replaced by what you type there. Now here comes a problem: with the subsup template in all apps except Word, the other dotted box vanishes. There’s a reason for this, but with hindsight, the implementation is pretty confusing as a number of users have noted via Send-a-Frown feedback (thanks for the feedback). The reason involves ease in entering hypergeometric functions, as explained below. But first note that the empty script can be entered: use the left or right arrow key to put the insertion point (IP) inside the empty script and type the desired text. In OneNote 2010, this is pretty sweet, since when the IP is inside an empty argument, the dotted box appears, inviting you to type something in (see Automatic Arguments). In PowerPoint 2010, the dotted box doesn’t appear. It was too hard to implement automatic arguments at the time we realized we needed it, but you can still type in the desired text. We’re very sorry for the confusion and heartily recommend you type in such things using the nice simple linear format J.
So how about the reason behind this “feature”, namely ease in entering confluent hypergeometric functions, which you probably do at least once a week. (Okay, you’ve never heard of them!) These functions have a pre subscript as well as a post subscript. The Office math rendering model has subscript, superscript, and subsup math objects for post scripts, but it only has the leftsubsup object for pre scripts. So to enter the hypergeometric-function pre subscript, you end up using a leftsubsup math object. In Word, the way to suppress the dotted box for the left superscript is to put a zero-width space (U+200B) into it. That’s a handy trick. You can type \zwsp to enter the U+200B, or you can type 200B followed by alt+x (in Word and OneNote) to enter it. Since this is kind of inconvenient, I came up with the approach that as soon as one script is entered, the dotted boxes for both scripts disappear. With hindsight, I realize we need richer subsup objects that don’t do this for the two subsup templates. And that richer object needs a file format extension, so it was postponed to Office 15.
The linear format for a simple confluent hypergeometric function is _1 F_2. The parser associates the _1 subscript with the base that follows (in this case F_2), unless the _1 directly follows some math variable. In this last case, if you want the _1 to associate with the base that follows, put a space before it and the space will be removed upon build up. There’s one more little problem: if you use a subscript instead of a subsup for the post subscript, it displays about one pixel higher than the pre subscript. Hopefully we can fix this in the next version. In the interim, use a left subsup for the pre subscript and a right subsup for the post subscript and, in Word, enter \zwsp in the corresponding superscripts to suppress the dotted boxes.