Allow erasing completed words
Currently, after a space is pressed, it's impossible to delete the space it or anything before it.
In practice, you want to correct typos immediately, since editing text afterwards takes so much time that it completely eliminates the benefits of typing fast in the first place. Typing tests should not get people into the habit of leaving typos in the text.
I propose that if backspace is pressed when the text input is empty (spacebar was just pressed), the previous entered word returns to the input so that it can be completed properly or corrected.