Well, I understood a case in which there was fixation downwards at the ties. The same only would be the case with friction clips if able to overcome all resulting slippage forces from temperature (and if so available and locked initial stresses such the prestress Denial refers to).
Of course if the expansion forces (or shortining ones) overcome friction you have one rail that is able to expand, in the extent that the standing restrictions allow. If such elongations were big, joints also need be -a problem-, or else what one needs to make is control expansion or shortening at the tie level, rather than for whole rails between joints.