code: function createContext(sentence) {
    const context = new Array(sentence.length + 4);
          context[0] = START[0];
          context[1] = START[1];
  
    for (let j = 0, m = sentence.length; j < m; j++)
      context[j + 2] = normalize(sentence[j][0]);
  
    context[context.length - 2] = END[0];
    context[context.length - 1] = END[1];
  
    return context;
  }
docs: Function used to build a context from the given tokenized sentence.
  
  @param  {array} sentence - Target sentence.
  @return {array}          - Context.