its very difficult to understand the crfsuite features

[paktiger]

anyone can assist me what is the mean of these features? And how we can customize it or add more features features = { 'bias': 1.0, 'word.lower()': word.lower(), 'word[-3:]': word[-3:], 'word[-2:]': word[-2:], 'word.isupper()': word.isupper(), 'word.istitle()': word.istitle(), 'word.isdigit()': word.isdigit(), 'postag': postag, 'postag[:2]': postag[:2],
} if i > 0: word1 = sent[i-1][0] postag1 = sent[i-1][1] features.update({ '-1:word.lower()': word1.lower(), '-1:word.istitle()': word1.istitle(), '-1:word.isupper()': word1.isupper(), '-1:postag': postag1, '-1:postag[:2]': postag1[:2], }) else: features['BOS'] = True

if i < len(sent)-1:
    word1 = sent[i+1][0]
    postag1 = sent[i+1][1]
    features.update({
        '+1:word.lower()': word1.lower(),
        '+1:word.istitle()': word1.istitle(),
        '+1:word.isupper()': word1.isupper(),
        '+1:postag': postag1,
        '+1:postag[:2]': postag1[:2],
    })
else:
    features['EOS'] = True