82. Extension Points

Here are the extension points that are available in Asciidoctor 0.1.4.

Preprocessor

Processes the raw source lines before they are passed to the parser.

TreeProcessor

Processes the Asciidoctor::Document (AST) once parsing is complete.

Postprocessor

Processes the output after the document has been converted, but before it’s written to disk.

DocinfoProcessor

Adds additional content to the header or footer regions of the generated document.

Block processor

Processes a block of content marked with a custom block style (i.e., [custom]). (similar to an AsciiDoc filter)

Block macro processor

Registers a custom block macro and processes it (e.g., gist::12345[]).

Inline macro processor

Registers a custom inline macro and processes it (e.g., Save).

Include processor

Processes the include::<filename>[] directive.

These extensions are registered per document using a callback that feels sort of like a DSL:

Asciidoctor::Extensions.register do |document|
  preprocessor FrontMatterPreprocessor
  tree_processor ShellSessionTreeProcessor
  postprocessor CopyrightFooterPostprocessor
  docinfo_processor TrackingCodeDocinfoProcessor if document.basebackend? 'html'
  block ShoutBlock
  block_macro GistBlockMacro if document.basebackend? 'html'
  inline_macro ManInlineMacro
  include_processor UriIncludeProcessor
end
Extension classes must be defined outside of the register block. Once an extension class is registered, it is frozen, preventing further modification. If you define an extension class inside the register block, it will result in an error on subsequent invocations.

You can register more than one processor of each type, though you can only have one processor per custom block or macro. Each registered class is instantiated when the Asciidoctor::Document is created.

There is currently no extension point for processing a built-in block, such as a normal paragraph. Look for that feature in a future Asciidoctor release.