This keyboard consist of 4 layers. first two layer is same as normal inscript or remington.

layer one - Direct key

layer two - shift + key

layer three - AltGr+key (AltGr = Right side Alt)

layer four - AltGr+shift+key

you can see the layout image below, in that

• left bottom - layer one
• left top - layer two
• right bottom - layer three
• right top - layer four
  

example

in Extended Inscript layout
in case of ’d’,
’d’ gives ്
‘Shift+d’ gives അ
‘Right Alt+d’ gives ഽ
‘Right Alt+Shift+d’ gives ഁ