Hi, this is not possible in SMath, or only with heavy workarounds.
I think you want something like this (as in Blockpad)

Also LibreOffice with the iMath-extension can produce such displays, yet you have to input some formatting codes in the formula editor.

Martin KraskaPre-configured portable distribution of SMath Studio: https://en.smath.info/wiki/SMath%20with%20Plugins.ashx