ROOT (token: short_text [lag_newlines/spaces] {pos_id})
 °--expr: a <-  [0/0] {1}                              
     ¦--expr: a [0/1] {3}                              
     ¦   °--SYMBOL: a [0/0] {2}                        
     ¦--LEFT_ASSIGN: <- [0/1] {4}                      
     °--expr: {1+1} [0/0] {5}                          
         ¦--'{': { [0/0] {6}                           
         ¦--expr: 1+1 [0/0] {7}                        
         ¦   ¦--expr: 1 [0/0] {9}                      
         ¦   ¦   °--NUM_CONST: 1 [0/0] {8}             
         ¦   ¦--'+': + [0/0] {10}                      
         ¦   °--expr: 1 [0/0] {12}                     
         ¦       °--NUM_CONST: 1 [0/0] {11}            
         °--'}': } [0/0] {13}                          
