 leaves both attributes unchanged within base.

   The msup element [...] increments scriptlevel by 1, and sets displaystyle to
   "false", within superscript, but leaves both attributes unchanged within
   base.

   The msubsup element [...] increments scriptlevel by 1, and sets displaystyle
   to "false", within subscript and superscript, but leaves both attributes
   unchanged within base.

   The mmultiscripts element increments scriptlevel by 1, and sets displaystyle
   to "false", within each of its a