Return the set of strategy functions from the {@link #errorStrategies errorStrategies collection}
that is appropriate for the field's {@link Ext.form.Labelable#msgTarget msgTarget} config.
function() {
        var me = this,
            owner = me.owner,
            strategies = me.errorStrategies,
            msgTarget = owner.msgTarget;
        return !owner.preventMark && Ext.isString(msgTarget) ?
                (strategies[msgTarget] || strategies.elementId) :
                strategies.none;
    }