In this rule

Historical Rules · 13 July 2018

Rule 701.31a

Official source text from the 13 July 2018 Rules release

Permalink

Some spells and abilities instruct players to vote for one choice from a list of options to determine some aspect of the effect of that spell or ability. To vote, each player, starting with a specified player and proceeding in turn order, chooses one of those choices.

Find this number in the current Rules