https://en.wikipedia.org/wiki/Help:Displaying_a_formula#Subscripts.2C_superscripts.2C_integrals proposes some hacks to attach scripts around a base:

(1) \sideset{_1^2}{_3^4}\prod_a^b

(2) {}_1^2\!\Omega_3^4

Note that the scripts "1" and "2" are not semantically attached to the base (but to a dummy "empty base"). Same for 3 and 4 in (1). Also (2) results in the generation of a negative space to do "as if" the prescripts were attached to the base. This is discouraged by the MathML spec (http://www.w3.org/TR/MathML/chapter3.html#presm.warnspacing).

These hacks are in particular problematic for assistive technologies.

The MathML spec has the <mmultiscripts> and <munderover> element for that purpose, see "multiscripts

& greek alphabet" on Joe Java's test http://eyeasme.com/Joe/MathML/MathML_browser_test

Note that itex2MML proposes the commands \tensor or \mmultiscripts to generate several pre/post scripts:

https://golem.ph.utexas.edu/~distler/blog/itex2MMLcommands.html#itex2MMLFrac