Set child for symbol 'A'.
Set child for symbol 'B'.
Set child for symbol 'C'.
Set child for symbol 'D'.
Found 'A': yes.
Does current exist? yes.
Current symbol 'A'.
Found 'B': yes.
Does current exist? yes.
Current symbol 'B'.
Found 'C': yes.
Does current exist? yes.
Current symbol 'C'.
Found 'D': yes.
Does current exist? yes.
Current symbol 'D'.
Found 'E': no.
Does current exist? no.