The option controls the counting rule. Y counts SO and SI within mixed strings as one each. N does not count the SO and SI and is the default.
DBRRIGHT('ab<.A.B>',4) -> 'ab'
DBRRIGHT('ab<.A.B>',3) -> 'ab<.A>'
DBRRIGHT('ab<.A.B>',5) -> 'a'
DBRRIGHT('ab<.A.B>',4,'Y') -> 'ab<.A>'
DBRRIGHT('ab<.A.B>',5,'Y') -> 'ab<.A>'
DBRRIGHT('ab<.A.B>',8) -> ''
DBRRIGHT('ab<.A.B>',8,'Y') -> ''