It would be very useful to have a command that hides text, and not just makes it invisible as in the spoiler feature. The reader can then toggle hide/unhide if they are interested in a certain level of detail.
A typical use of this function would be for mathematical question:
Q: How can I calculate this complicated integral ....?
A: 1) Complete the square in the exponent.
hidetext: Detailled messy calculation.
2) Change variable $x$ to $x-2$.
hidetext: More details.
3) Use the formula for the Gaussian integral to get the result ...
hidetext: Details on this calculation plus weblink on Gaussian integral.
This is an example of another forum of what this can look like (click on the word Casework):