docs: public void write(Collection<? extends MapLayer> layers) throws IOException {
  		if (this.progression != null) {
  			this.progression.setProperties(0, 0, layers.size() + 1, false);
  		}
  
  		// Write the header
  		if (!this.isHeaderWritten) {
  			this.isHeaderWritten = true;
  			writeHeader();
  		}
  
  		if (this.progression != null) {
  			this.progression.increment();
  		}
  
  		final ObjectOutputStream oos = new ObjectOutputStream(this.tmpOutput);
  		for (final MapLayer layer : layers) {
  			oos.writeObject(layer);
  			++this.length;
  			if (this.progression != null) {
  				this.progression.increment();
  			}
  		}
  		if (this.progression != null) {
  			this.progression.end();
  		}
  	}