What are parser hooks, and how do they work?
Parser Hooks are, well, hooks that enable assembly programs to do some things. They can not be used in any way by TI-BASIC.
I have some slight idea of their nature: they run in the background. Do they take up any valuable clock cycles?
They don't run in the background - you're thinking of interrupts. Parser hooks are called whenever a TI-Basic expression is calculated, or "parsed" - thus the name. In practice, usually a parser hook would check if the expression uses a specific command, and quit otherwise, taking up a minimum of time. Executing even a simple TI-Basic command takes thousands of clock cycles, so the few that this process takes up make no difference.
hey, wouldn't it be cool if someone used interrupts to capture the screen on the calc and put it in some format.
Then, A computer program could use what was created to make a video.
The only problem would be getting around Disable interrupts.