Why do signals have multiple multiplexer values?

[bmcpt]

Signals have a field signal_multiplexer_values which is a vector: https://github.com/xR3b0rn/dbcppp/blob/067abf5609788b24626ab9b496aa96d4b5d252a5/src/libdbcppp/SignalImpl.h#L88

But when I open a DBC file in candb++, it only allows me to set a single multiplexer for each signal. What is the reason for making this field a vector?