Bullet represets a '*' non-adjacent to text.

CloseBracket represents a ')', ']' or '}'.

Emphasis represets a '*', '_', '**' or '__' adjacent text.

Heading represents a run of '#'.

NewLine represents a newline.

OpenBracket represents a '(', '[' or '{'.

Tag represents a alpha-numeric wrapped with double curly brackets.

Text represents regular text.

Token is the interface implemented by all tokens.