Last week, a flurry of litigation in Pennsylvania clarified the rules for mail balloting there. In short, mail ballots will still be rejected in the key battleground state if voters fail to properly date the affidavits that accompany their ballots — but voters who make any mistake with their mail ballots will be able to vote by provisional ballot instead on Election Day.

A provisional ballot is a safeguard ballot that lets voters cast a vote even if there are questions about eligibility.