* @param unit The <code>Unit</code> that is learning.
     * @param settlement The <code>Settlement</code> to learn from.
     * @return An <code>Element</code> encapsulating this action.
     */
    public Element askLearnSkill(ServerPlayer serverPlayer, Unit unit,
                                 IndianSettlement settlement) {
        ChangeSet cs = new ChangeSet();

        csSpeakToChief(serverPlayer, settlement, false, cs);
        Tile tile = settlement.getTile();
        tile.updatePlayerExploredTile(serverPlayer, true);
        cs.add(See.only(serverPlayer), tile);
        unit.setMovesLeft(0);
        cs.addPartial(See.only(serverPlayer), unit, "movesLeft");

        // Do not update others, nothing to see yet.
        return cs.build(serverPlayer);
    }