While a voter may choose to, there is no requirement to study any source beyond the precise part(s) quoted or paraphrased by either debater (and even then, within reason). Further, overly studying a source beyond what was presented, risks basing a vote upon the outside content of your own analysis instead of that offered by the debaters. If neither debater even alluded to details from a source a voter mentions, the vote has probably crossed this line. The one exception where it is acceptable to do this would be a situation in which the voter notices one side blatantly lying about what is present in their source (even if that criticism wasn’t brought up by the opponent). Note that this does not include implied warrants (For example, Debater A gives a statistic of rising temperatures and says “this source supports my argument that people will be eating more ice cream in the years to come”... The warrant here is implied, not explicitly stated. The voter should not use this as an excuse to say Debater A lied about the contents of the source).