Block represents a collection of nodes in sequential order.

Emphasis represents a emphasis node.

Heading represents a heading node.

Link represents a link in the form: [body](target).

NewLine represents a blank new line.

Tag represents a tag in the form: {{identifier:type}}, where "type" is optional and is "string" by default.

Text represent a block of text.

Whitespace represent a whitespace.

Node represents a node in a minidown document graph.