Default Selection for list box

[manideep78]

Hi All

How can I select all values in list box by default.?? 

If I select any value in the list box that particular value needs to be selected but If I uncheck the selected option, all values should be selected by default.

any help will be appreciated

Regards,

Manideep

[Nicole-Smith]

What do you mean by special symbols?  Can you tell me what the values are/look like?