If a web page contains a text area along with some other content around it (such as the Body text area on the Stack Exchange "Ask question" page), then it's possible scroll up and down in this text area by placing the mouse pointer over it and using the scroll up/down gesture on the trackpad of my MacBook.
I want to emulate this gesture using the keyboard, so I just have to place the mouse pointer over the text area and use a keyboard shortcut to scroll up and down in this text area.
How do I achieve this?
Note: I'm aware that it's possible to click on the text area, in order to bring it in focus (so that I can type in text), after which I can move the cursor in the text area using the keyboard (which also has the effect of scrolling up/down as the cursor is followed). But this is not what I'm interested in.