Hi. It's a simple mistake.
In line 37 of sdlkeycode.inc
SDLK_QUOTE = TSDL_KeyCode('\');
must be
SDLK_QUOTE = TSDL_KeyCode('''');
Backslash \ key is defined in line 67: SDLK_BACKSLASH = TSDL_KeyCode('\');
Actually, SDLK_QUOTE was renamed three week ago to SDLK_APOSTROPHE, but I'think that it's for SDL3