Xtext outline view using grammar and Xtend

Question

How to get outline view in Xtext using Xtend for this particular parser rule written in Xtext?

def_slotted_exemplar:   
       ex= Exemplar (':'name=ID )
        ','
    (   '{}' |( ('{}'',') ('{}' | inht=Inherit | val=inherit_validation))|
        ('{' ('}' | ( ('}'',')
        ('{}' | inht=Inherit | val=inherit_validation)))) |
        ('{' ((cls=classvariable) | (val=def_validation)) ('}' | ( ('}'',')
        ('{}' | inht=Inherit | val=inherit_validation))))                  
    )

    ')'
    '$'
    ;