#141 Mouse button keyname

[harshash]

I'm creating custom keymap, instead of keys from keyboad. I want to used mouse buttons.
on xterm I know the keyname for mouse buttons eg: <Btn4Down>, <Btn5Down>...

Can anyone please tell me what are the keyname for mouse buttons in mrxvt.

Mrxvt.macro.Primary+Button3: Str . handle %s \n

I tried RMB, LMB, Button3 amd many more, I can't find the right name for mouse button.