Multilevel Subscripts in Equations

**The package I want to suggest the idea to**: AngouriMath
It would be useful if equations could have multiple levels of subscript. This is particularly useful for equations that come from technical papers where subscripts can often be multiple levels deep.

for example something similar to the following code would be a valid equation.
`Entity expr = "X_a_beta + 10"`

It would also be great if the `.Latexise()` function worked on these equations as well.