difference between 1.4v PCML and 1.5v PCML

What is the difference between 1.4v PCML and 1.5v PCML in Stratix5? How do I know which one should be used for a given developement board, for example the Transceiver Signal Integrity Development Kit? I know it is listed as 1.4v PCML in the reference manual. But why it is not 1.5v PCML? I thought it is difined by GXB power supply pins like VCCH_GXB, VCCR_GXB, or VCCT_GXB. But it seems not the case when I checked the schematics.