petition_change_movement_power_effect

petition_change_movement_power_effect = {
	save_scope_value_as = {
		name =  petition_modifies_movement_power_value
		value = $VALUE$
	}
	if = {
		limit = {
			NOT = {
				participant_group_type = undecided_movement
			}
		}
		if = {
			limit = {
				$VALUE$ >= 0
			}
			custom_tooltip = {
				text = petition_increase_movement_power_effect_tooltip
				if = {
					limit = {
						exists = var:movement_power_increased_petition
					}
					set_variable = {
						name = movement_power_increased_petition
						value = {
							value = var:movement_power_increased_petition
							add = $VALUE$
						}
					}
				}
				else = {
					set_variable = {
						name = movement_power_increased_petition
						value = $VALUE$
					}
				}
			}
		}
		else = {
			custom_tooltip = {
				text = petition_decrease_movement_power_effect_tooltip
				if = {
					limit = {
						exists = var:movement_power_decreased_petition
					}
					set_variable = {
						name = movement_power_decreased_petition
						value = {
							value = var:movement_power_decreased_petition
							add = $VALUE$
						}
					}
				}
				else = {
					set_variable = {
						name = movement_power_decreased_petition
						value = $VALUE$
					}
				}
			}
		}
		#force the update of variables to immediately show changes
		if = { #for characters
			limit = {
				exists = var:movement_power_individual
			}
			update_character_movement_power_effect = yes
			top_participant_group:dynastic_cycle ?= {
				update_movement_power_effect = yes
			}
		}
		else = { #for movements
			update_movement_power_effect = yes
		}
	}
}

As written in game/common/scripted_effects/10_dlc_tgp_scripted_effects.txt.