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