change_artifact_book_content_quality_effect

change_artifact_book_content_quality_effect = {
	if = {
		limit = {
			$AMOUNT$ > 0
		}
		custom_tooltip = change_artifact_book_content_quality_effect_gain
	}
	else_if = {
		limit = {
			$AMOUNT$ < 0
		}
		custom_tooltip = change_artifact_book_content_quality_effect_loss
	}
	hidden_effect = {
		if = {
			limit = {
				NOT = {
					exists = var:book_content_quality
				}
			}
			set_variable = {
				name = book_content_quality
				value = $AMOUNT$
			}
		}
		else = {
			change_variable = {
				name = book_content_quality
				add = $AMOUNT$
			}
		}
	}
}

As written in game/common/scripted_effects/01_ep1_court_artifact_creation_effects.txt.