direction_x, direction_y, direction_z
Required for directional and spot lights, indicate the direction vector pointing 
from the light source to the light target. The length of the vector is 
unimportant, as it does not carry further information. If both direction 
and position parameters are missing when creating a light, an error is shown.
Example: <light ... direction_x="0.0" direction_y="0.0" direction_z="-1.0"/> (default)
(Defined in GAMGI_MESA_LIGHT_DIRECTION_X, GAMGI_MESA_LIGHT_DIRECTION_Y
and GAMGI_MESA_LIGHT_DIRECTION_Z)
Allowed values: real (required, coupled)
position_x, position_y, position_z
Required for positional and spot lights, indicate the position coordinates from 
where the light is emitting. If both direction and position parameters are 
missing when creating a light, an error is shown.
Example: <light ... position_x="0.0" position_y="0.0" position_z="10.0"/> (default)
(Defined in GAMGI_MESA_LIGHT_POSITION_X, GAMGI_MESA_LIGHT_POSITION_Y
and GAMGI_MESA_LIGHT_POSITION_Z)
Allowed values: real (required, coupled)
angle
Required for spot lights, indicates the angle from the spot 
direction to the outer surface of the conic beam.
Example: <light ... angle="90.0"/> (default)
(Defined in GAMGI_MESA_LIGHT_ANGLE)
Allowed values: 0.0 < real <= 90.0 (optional)