Change content according to user input

I want to create a cooking book where the user can write in a entry field for how many people he wants to cook. Then the recipe has to show the recalculated amount of ingredients on screen and also on the screenreader.
Similar use cases can be found for textbooks.

No file, test, or entry point is named in the issue. Start by clarifying the cooking-book interaction and its textbook applicability, including screen-reader behavior; define completion as agreed requirements for entering a people count and presenting recalculated ingredient amounts visibly and audibly.

Written by the indexing model from the issue text.