How to validate custom page buttons using INSTALLOPTIONS

I use !insertmacro MUI_INSTALLOPTIONS_DISPLAY "sample_config.ini" to display a custom page,but i dont know how to check whether user clicked back,cancel,i dont use leave function i just show the custom page say Page custom Sample_Readme and inside Sample_Readme function i do the validations.

!insertmacro MUI_INSTALLOPTIONS_DISPLAY_RETURN "sample_config.ini"
Pop $R0
MessageBox MB_OK "$R0"
will return the value.
Refer http://forums.winamp.com/printthread...hreadid=182393