drawOver(x, y, ch, fg, bg) {
        const key = `${x},${y}`;
        const existing = this._data[key];
        if (existing) {
            existing[2] = ch || existing[2];
            existing[3] = fg || existing[3];
            existing[4] = bg || existing[4];
        }
        else {
            this.draw(x, y, ch, fg, bg);
        }
    }
@param {int} x
@param {int} y
@param {string || string[]} ch One or more chars (will be overlapping themselves)
@param {string || null} [fg] foreground color
@param {string || null} [bg] background color