code: function(sourceFormats, targetFormats) {
          targetFormats = targetFormats || this.formats;
          for (var f in sourceFormats) {
              if (f in targetFormats) {
                  return f;
              }
          }
      }
docs: Method: findMimeType
  Finds a supported mime type.
  
  Parameters:
  sourceFormats - {Object} An object literal with mime types as key and
  true as value for supported formats.
  targetFormats - {Object} Like <sourceFormats>, but optional to check for
  supported mime types on a different target than this process.
  Default is to check against this process's supported formats.
  
  Returns:
  {String} A supported mime type.