I want SPACE+Mbutton to send another button without stopping space function

Question

I want my script to send another button when I press both spacebar and middle mouse button. However, I also want the spacebar to work normally when only space is pressed (i.e. it makes spaces as normal).

I've tried the script below and "space + middle mouse button" does send 9, but space doesn't work when only space is pressed (it doesn't make spaces).

SPACE & MButton:: Send 9

Answer 1

This two sentences together do the job pretty well:

 Space & MButton::Send 9
 Space::Send, {SPACE}

Answer 2

You can preserve a key's functionality with the ~ hotkey modifier

When the hotkey fires, its key's native function will not be blocked (hidden from the system).

So to preserve the spacebar's functionality, your hotkey would be:

~Space & MButton::Send 9