Documentation specification (#4294)

docs/README.md

@@ -67,3 +67,131 @@ It should build the static app that will be available under `/docs/_build/html`
 
 Accepted files are reStructuredText (.rst) and Markdown (.md). Create a file with its extension and put it
 in the source directory. You can then link it to the toc-tree by putting the filename without the extension.
+
+## Writing Documentation - Specification
+
+The `huggingface/transformers` documentation follows the
+[Google documentation](https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html) style. It is
+mostly written in ReStructuredText 
+([Sphinx simple documentation](https://www.sphinx-doc.org/en/master/usage/restructuredtext/index.html), 
+[Sourceforge complete documentation](https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html))
+
+### Adding a new section
+
+A section is a page held in the `Notes` toc-tree on the documentation. Adding a new section is done in two steps:
+
+- Add a new file under `./source`. This file can either be ReStructuredText (.rst) or Markdown (.md).
+- Link that file in `./source/index.rst` on the correct toc-tree.
+
+### Adding a new model
+
+When adding a new model:
+ 
+- Create a file `xxx.rst` under `./source/model_doc`. 
+- Link that file in `./source/index.rst` on the `model_doc` toc-tree.
+- Write a short overview of the model:
+    - Overview with paper & authors
+    - Paper abstract
+    - Tips and tricks and how to use it best
+- Add the classes that should be linked in the model. This generally includes the configuration, the tokenizer, and
+  every model of that class (the base model, alongside models with additional heads), both in PyTorch and TensorFlow.
+  The order is generally: 
+    - Configuration, 
+    - Tokenizer
+    - PyTorch base model
+    - PyTorch head models
+    - TensorFlow base model
+    - TensorFlow head models
+
+These classes should be added using the RST syntax. Usually as follows:
+```
+XXXConfig
+~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.XXXConfig
+    :members:
+```
+
+This will include every public method of the configuration. If for some reason you wish for a method not to be displayed
+in the documentation, you can do so by specifying which methods should be in the docs:
+
+```
+XXXTokenizer
+~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.XXXTokenizer
+    :members: build_inputs_with_special_tokens, get_special_tokens_mask,
+        create_token_type_ids_from_sequences, save_vocabulary
+
+```
+
+### Writing source documentation
+
+Values that should be put in `code` should either be surrounded by double backticks: \`\`like so\`\` or be written as an object
+using the :obj: syntax: :obj:\`like so\`.
+
+When mentionning a class, it is recommended to use the :class: syntax as the mentioned class will be automatically
+linked by Sphinx: :class:\`transformers.XXXClass\`
+
+When mentioning a function, it is recommended to use the :func: syntax as the mentioned method will be automatically
+linked by Sphinx: :func:\`transformers.XXXClass.method\`
+
+Links should be done as so (note the double underscore at the end): \`text for the link <./local-link-or-global-link#loc>\`__
+
+#### Defining arguments in a method
+
+Arguments should be defined with the `Args:` prefix, followed by a line return and an indentation. 
+The argument should be followed by its type, with its shape if it is a tensor, and a line return.
+Another indentation is necessary before writing the description of the argument.
+
+Here's an example showcasing everything so far:
+
+```
+    Args:
+        input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`):
+            Indices of input sequence tokens in the vocabulary.
+
+            Indices can be obtained using :class:`transformers.AlbertTokenizer`.
+            See :func:`transformers.PreTrainedTokenizer.encode` and
+            :func:`transformers.PreTrainedTokenizer.encode_plus` for details.
+
+            `What are input IDs? <../glossary.html#input-ids>`__
+```
+
+#### Writing a multi-line code block 
+
+Multi-line code blocks can be useful for displaying examples. They are done like so:
+
+```
+Example::
+
+    # first line of code
+    # second line
+    # etc
+```
+
+The `Example` string at the beginning can be replaced by anything as long as there are two semicolons following it.
+
+#### Writing a return block
+
+Arguments should be defined with the `Args:` prefix, followed by a line return and an indentation. 
+The first line should be the type of the return, followed by a line return. No need to indent further for the elements
+building the return.
+
+Here's an example for tuple return, comprising several objects:
+
+```
+    Returns:
+        :obj:`tuple(torch.FloatTensor)` comprising various elements depending on the configuration (:class:`~transformers.BertConfig`) and inputs:
+        loss (`optional`, returned when ``masked_lm_labels`` is provided) ``torch.FloatTensor`` of shape ``(1,)``:
+            Total loss as the sum of the masked language modeling loss and the next sequence prediction (classification) loss.
+        prediction_scores (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, config.vocab_size)`)
+            Prediction scores of the language modeling head (scores for each vocabulary token before SoftMax).
+```
+
+Here's an example for a single value return:
+
+```
+    Returns:
+        A list of integers in the range [0, 1]: 1 for a special token, 0 for a sequence token.
+```