strict (0 or TRUE, or omitted): Use the most strict classical rules. When a smaller numeral precedes a larger to indicate subtraction, the smaller must be a power of 10 and can precede a number no more than 10 times its size. For example, 999 is represented as CMXCIX, but not LMVLIV.
relax by one degree (1): Relax the strict classical rule by one degree. When a smaller number precedes a larger, the smaller need not be a power of 10 and the relative size rule is extended by one numeral. For example, 999 can be represented as LMVLIV, but not XMIX.
relax by two degrees (2): Relax the classical rule by two degrees. When a smaller number precedes a larger, the relative size rule is extended by two numerals. For example, 999 can be represented as XMIX, but not VMIV.
relax by three degrees (3): Relax the classical rule by three degrees. When a smaller number precedes a larger, the relative size rule is extended by three numerals. For example, 999 can be represented as VMIV, but not IM.
relax by four degrees (4 or FALSE): Relax the classical rule by four degrees. When a smaller number precedes a larger, the relative size rule is extended by four numerals. For example, 999 can be represented as IM.
Examples
=ROMAN(12) returns XII.
=ROMAN(999) returns CMXCIX.
=ROMAN(999, 1) returns LMVLIV.
=ROMAN(999, 2) returns XMIX.
=ROMAN(999, 3) returns VMIV.