where operator using a saved equation?

[smm9509]

> my_equation := "a" = 2

  save(a = 2, my_equation)

  a = 2

> "a" + 5 where my_equation

  a + 5 = a + 5

> "a" + 5 where "a" = 2 #expected answer

  a + 5 = 7

I want to substitute using the solution found earlier in the process and saved. Should also work with the output of solve/multisolve.

(Also, the documentation for the where operator has been elusive until version 5.0.0, I didn't know it existed until it showed up in the release notes. How to discover qalc features easier?)