# 9 EEP-48: Implementation in Erlang/OTP

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9.1 EEP-48: Documentation storage and format

EEP-48 defines a common documentation storage format for module documentation in the Erlang/OTP ecosystem. Erl_Docgen can generate documentation in this format from XML files following the DTD's descibed in the other User's Guides in this application.

Some special considerations have to be taken when writing documentation that should also be available through EEP-48 style storage.

- The #PCDATA within <name> tags must be parseable to figure out the arity of the function.
- It is not allowed to mix <name> tags with #PCDATA and attributes.
- All <name> tags within <func> has to have a since attribute.
- All callback function documentations have to start with a Module prefix.

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9.2 Erlang Documentation Format

When generating documentation for EEP-48 Erl_Docgen uses the format mime type <<"application/erlang+html">>. The documentation content is an Erlang term that represents an HTML like structure.

    -type chunk_elements() :: [chunk_element()].
    -type chunk_element() :: {chunk_element_type(),chunk_element_attrs(),
                              chunk_elements()} | unicode:unicode_binary().
    -type chunk_element_attrs() :: [chunk_element_attr()].
    -type chunk_element_attr() :: {atom(),unicode:unicode_binary()}.
    -type chunk_element_type() :: chunk_element_inline_type() | chunk_element_block_type().
    -type chunk_element_inline_type() :: a | code | strong | b | em | i.
    -type chunk_element_block_type() :: p | 'div' | br | pre | ul |
                                        ol | li | dl | dt | dd |
                                        h1 | h2 | h3 | h4 | h5 | h6.

The different element types follow their HTML meaning when rendered. The following are some general rules for how the chunk elements are allowed to be generated.

- Inline and pre elements are not allowed to contain block elements.
- p elements are not allowed to be nested.

The attributes on some elements have a special meaning.

{'div',[{class,unicode:unicode_binary()}],_}
  The class name will be used to provide styling to the content in the div. The types of classes used by Erlang/OTP are: warning, note, do, dont and quote.
{ul,[{class,<<"types">>}],_}
  This is a list containing type documentation.
{li,[{name,TypeName :: unicode:unicode_binary()}],_}
  A list item with a type specification located in the metadata of this modules EEP-48 documentation. The implementation should look for the AST representation of the type under the types key. This attribute is only valid under a ul with class <<"types">>.
{li,[{class,<<"type">>}],_}
  A list item with the type described in the Erlang Documentation Format. This attribute is only valid under a ul with class <<"types">>.
{li,[{class,<<"description">>}],_}
  A list item with the description of the type previous in the list. This attribute is only valid under a ul with class <<"types">>.

The shell_docs:validate/1 function can be used to do a validation of the Erlang Documentation Format.

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9.3 Erlang Documentation extra Metadata

Erlang/OTP uses some extra metadata fields to embed more information into the EEP-48 docs.

- Fields on module level:
  otp_doc_vsn := {non_neg_integer(),non_neg_integer(),non_neg_integer()}
    Describes the version of the Erlang Documentation Format used within this module
  types := #{ TypeName :: unicode:unicode_binary() => TypeAST }
    A map containing the AST of the types that are part of this module. This map is used to by functions and callbacks to render the types inline into their documentation.
- Fields on functions and types:
  signature := SpecAST
    The spec AST associated with this function. It is used to render a more descriptive slogan for the documentation entry.
  equiv := {Type,Name,Arity}
    The current function/type shares documentation with another function/type. This means that if this and the target function/type are to be shown at the same time only the prototype of this function/type should will be displayed and the documentation will use a common body of text.

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9.4 See Also

shell_docs(3), code:get_doc(3)