Online Algebra Calculator
Many of users do not use powerful Maxima computer algebra system for systematic work, but for ad hoc algebraic calculations – equations, functions, matrixes, etc. only. To do this job, it is not useful to download the whole application from a web site.
Function: dpart (<expr>, <n_1>, ..., <n_k>) Selects the same subexpression as part, but instead of just returning that subexpression as its value, it returns the whole expression with the selected subexpression displayed inside a box. The box is actually part of the expression.

(%i1) dpart (x+y/z^2, 1, 2, 1);
y
(%o1) ---- + x
2
"""
"z"
"""(%o1) true (%i2)