addButtons {1,1 8 {Button_1 action_1} {Button_2 action_2} {} {Button_3 action_3}}

Note: A null button item will display a five character (the default pad size) gap in the Button row.

addButtons {1,1 8 10 {Button_1 action_1} {Button_2 action_2} {} {Button_3 action_3}}
...or...
addButtons {1,1 8 {Button_1 action_1} {Button_2 action_2} {10} {Button_3 action_3}}

Note: Specifying 10 as the pad size sets the "null" Button item gap to ten characters.

addButtons {1,1 8 {Button_1 action_1} {Button_2 disabled action_2} {} {Button_3 action_3}}
...or...
addButtons {1,1 8 {Button_1 action_1} {-Button_2 action_2} {} {Button_3 action_3}}

Note: Button item options can be specified for each Button item, in this case disabled for Button_2.