GridLayer

• createTile must call done with an error and tile for async content so load events fire.
• maxNativeZoom stretches the highest available tiles instead of requesting missing levels.
• keepBuffer controls how many off-screen tile rings stay cached in memory.

var LabelGrid = L.GridLayer.extend({
  createTile: function (coords) {
    var tile = L.DomUtil.create('canvas', 'leaflet-tile');
    var size = this.getTileSize();
    tile.width = size.x;
    tile.height = size.y;

    var ctx = tile.getContext('2d');
    ctx.fillStyle = '#f4f6f8';
    ctx.fillRect(0, 0, size.x, size.y);
    ctx.strokeStyle = '#d5dae1';
    ctx.strokeRect(0.5, 0.5, size.x - 1, size.y - 1);

    ctx.fillStyle = '#58606e';
    ctx.font = '12px sans-serif';
    ctx.fillText(coords.z + '/' + coords.x + '/' + coords.y, 10, 20);

    return tile;
  }
});

var labels = new LabelGrid({ tileSize: 256, opacity: 0.9 }).addTo(map);
labels.on('tileerror', function (e) { console.warn(e.coords, e.error); });

• Skipping the done callback on async tiles leaves isLoading permanently true.
• Leaving maxNativeZoom unset above the provider limit produces blank screens at high zoom.