Keras Parameters for Convolutional Net

I'm looking at Keras' example for convolutional neural networks. (See https://github.com/fchollet/keras/blob/master/examples/imdb_cnn.py for example.) However, I cannot figure out what they mean by the "maxlen" parameter. Would it have something to do with padding? It isn't the maximum number of features; they have a max_features parameter for that.