Quick question relative item syntax - specifying an unknown/common item {?;+1}

Hello folks, 

I am a big fan of the relative item component, however my question is how do you specify an unknown/common data item. 

i.e. I want to write 

{?;+1} however I am getting an error based on an invalid mask, 

I have also tried {0;+1} in my specific case, but this is more of a general question. 

Also is you have various data structures 

ie. 

{0;0;0}

{0;0}

{0;0;0;0;0;0} 

can these all be fed into one relative item component to deal with only the say the last two structure items (i.e. the final two branches)

Many thanks

J-P