INPUT 100-240VAC - will it only work with Voltage Rating within 100-240 ?
This means that the manufacturer "guarantees" that the product can work with input voltages between 100 and 240Vac. Of course there are some tolerances, but this range is "guaranteed". 

You know, since those type of chargers are off-line flyback switching regulators, lower input voltage increases input current and higher input voltage increases spikes. So the product should not be damaged under these conditions. Besides, I'm sure that these type of products are tested with extreme voltage levels (Let's assume that 85-265Vac for 1 hr @ 50°C). So yes, they can work either with >240V or &lt;100V, but within some (say, %10) tolerance.