code: function loadMaki(options, callback) {
      var base = options.base + '-' + options.size + (options.retina ? '@2x' : ''),
          size = options.size,
          symbol = options.symbol + '-' + sizes[size] + (options.retina ? '@2x' : '');
  
      if (!base || !size) {
          return callback(errcode('Marker is invalid because it lacks base or size.', 'EINVALID'));
      }
  
      if (!makiAvailable[symbol]) {
          return callback(errcode('Marker symbol "' + options.symbol + '" is invalid.', 'EINVALID'));
      }
  
      fs.readFile(makiRenders + symbol + '.png', function(err, data) {
          if (err) return callback(new Error('Marker "' + JSON.stringify(options) + '" is invalid because the symbol is not found.'));
  
          // Base marker gets tint applied.
          var parts = [{
              buffer: markerCache.base[base],
              tint: options.parsedTint
          }];
  
          // If symbol is present, find correct offset (varies by marker size).
          if (symbol) {
              parts.push(xtend({
                  buffer: data,
                  tint: blend.parseTintString('0x0;0x0;1.4x0'),
              }, offsets[size + (options.retina ? '@2x' : '')]));
          }
  
          // Add mask layer.
          parts.push({
              buffer: markerCache.mask[base]
          });
  
          // Extract width and height from the IHDR. The IHDR chunk must appear
          // first, so the location is always fixed.
          var width = markerCache.base[base].readUInt32BE(16),
              height = markerCache.base[base].readUInt32BE(20);
  
          // Combine base, (optional) symbol, to supply the final marker.
          blend(parts, {
              format: 'png',
              quality: 256,
              width: width,
              height: height
          }, function(err, data) {
              if (err) return callback(err);
              return callback(null, data);
          });
      });
  }
docs: Load & composite a marker from the maki icon set.
  
  @param {object} options
  @param {function} callback