turning labels into a vector

Hello


1/ 'priors' is a table looking like:

"W123" "T678" "S789"
  23          42       11
  12          35         9
etc

2/ WBS <- labels(priors) gives me a result of class list and length 
1 looking like:

"W123" "T678" "S789"



I want to read W123 into X[1] as W, T687 into X[2] as T and S789 
into X[3] as S using substr(X[1],1,1) but I'm having trouble 
extracting each group of 4 digits from WBS

Any help would be gratefully accepted.

thanks
Meredith