Asmc Macro Assembler Reference
OPTION SETIF2:[TRUE|FALSE]
If TRUE, .ERR2 statements and IF2 and ELSEIF2 conditional blocks are evaluated on every pass. If FALSE, they are not evaluated. If SETIF2 is not specified (or implied), .ERR2, IF2, and ELSEIF2 expressions cause an error. Both the /Zm command-line argument and OPTION M510 imply SETIF2:TRUE.