Training
[LongformerForMaskedLM] is trained the exact same way [RobertaForMaskedLM] is
trained and should be used as follows:
thon
input_ids = tokenizer.encode("This is a sentence from [MASK] training data", return_tensors="pt")
mlm_labels = tokenizer.encode("This is a sentence from the training data", return_tensors="pt")
loss = model(input_ids, labels=input_ids, masked_lm_labels=mlm_labels)[0]

Resources

Text classification task guide
Token classification task guide
Question answering task guide
Masked language modeling task guide
Multiple choice task guide

LongformerConfig
[[autodoc]] LongformerConfig
LongformerTokenizer
[[autodoc]] LongformerTokenizer
LongformerTokenizerFast
[[autodoc]] LongformerTokenizerFast
Longformer specific outputs
[[autodoc]] models.longformer.modeling_longformer.LongformerBaseModelOutput
[[autodoc]] models.longformer.modeling_longformer.LongformerBaseModelOutputWithPooling
[[autodoc]] models.longformer.modeling_longformer.LongformerMaskedLMOutput
[[autodoc]] models.longformer.modeling_longformer.LongformerQuestionAnsweringModelOutput
[[autodoc]] models.longformer.modeling_longformer.LongformerSequenceClassifierOutput
[[autodoc]] models.longformer.modeling_longformer.LongformerMultipleChoiceModelOutput
[[autodoc]] models.longformer.modeling_longformer.LongformerTokenClassifierOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerBaseModelOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerBaseModelOutputWithPooling
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerMaskedLMOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerQuestionAnsweringModelOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerSequenceClassifierOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerMultipleChoiceModelOutput
[[autodoc]] models.longformer.modeling_tf_longformer.TFLongformerTokenClassifierOutput

LongformerModel
[[autodoc]] LongformerModel
    - forward
LongformerForMaskedLM
[[autodoc]] LongformerForMaskedLM
    - forward
LongformerForSequenceClassification
[[autodoc]] LongformerForSequenceClassification
    - forward
LongformerForMultipleChoice
[[autodoc]] LongformerForMultipleChoice
    - forward
LongformerForTokenClassification
[[autodoc]] LongformerForTokenClassification
    - forward
LongformerForQuestionAnswering
[[autodoc]] LongformerForQuestionAnswering
    - forward

TFLongformerModel
[[autodoc]] TFLongformerModel
    - call
TFLongformerForMaskedLM
[[autodoc]] TFLongformerForMaskedLM
    - call
TFLongformerForQuestionAnswering
[[autodoc]] TFLongformerForQuestionAnswering
    - call
TFLongformerForSequenceClassification
[[autodoc]] TFLongformerForSequenceClassification
    - call
TFLongformerForTokenClassification
[[autodoc]] TFLongformerForTokenClassification
    - call
TFLongformerForMultipleChoice
[[autodoc]] TFLongformerForMultipleChoice
    - call