Effective value of the Register type may contain AX as selected field, but discriminator value may be either `a` or `b` and it is stored in memory separately. Therefore, IDL logically separates information about currently selected field name and union effective value from information about current discriminator value. In the example above, dis... Found on http://en.wikipedia.org/wiki/Discriminator
a person or thing that discriminates. · a circuit in which the output is a function of some variation of an input signal from a fixed characteristic. Found on https://www.infoplease.com/dictionary/discriminator