setIdentifier(id = "") {
        if (id.length === 0) return;
        this.identifier = id;
        const len = this.identifier.length;
        if (len === 1) this.xSize = 20;
        else if (len > 1 && len < 4) this.xSize = 10;
        else this.xSize = 0;
    }
@memberof Flag
set the flag id
@param {number} id - identifier for flag