ROOT (token: short_text [lag_newlines/spaces] {pos_id})
 ¦--expr: a [0/0] {2}                                  
 ¦   °--SYMBOL: a [0/0] {1}                            
 °--expr: b [1/0] {4}                                  
     °--SYMBOL: b [0/0] {3}                            
