docs: function concat(attributeDictionary, attribute) {
    expect(arguments).to.have.length(
      2,
      'Invalid arguments length when concatenating an AttributeDictionary (it ' +
      'has to be passed 2 arguments)'
    );
  
    expect(attributeDictionary).to.be.instanceof(
      AttributeDictionary,
      'Invalid argument "attributeDictionary" when concatenating an ' +
      'AttributeDictionary (it has to be an AttributeDictionary)'
    );
  
    expect(attribute).to.be.instanceof(
      Attribute,
      'Invalid argument "attribute" when concatenating an AttributeDictionary ' +
      '(it has to be an Attribute)'
    );
  
    var currentAttributes = [];
  
    for (var currentAttribute in attributeDictionary) {
      currentAttributes.push(attributeDictionary[currentAttribute]);
    }
  
    currentAttributes.push(attribute);
  
    return new AttributeDictionary(currentAttributes);
  }