Details on Dwarf Sexuality: http://dwarffortresswiki.org/index.php/DF2014:Marriage
The token takes 4 arguments: [ORIENTATION:<male/female>:<disinterested chance>:<lover-possible chance>:<commitment-possible chance>]. A one-time check is made for each creature to determine orientation, by "rolling a die" once for each sex, against the total of the three chances for that sex.
If a given dwarf rolls "disinterested" for the same sex, and "commitment-possible" for the opposite sex, then that dwarf is strictly heterosexual, and is willing to become married. If the dwarf rolls "lover-possible" for each sex, then the dwarf is bisexual, but will never marry. And so on.