We store the lines we’re working on as objects of class Line. These contain the text of the line, along with a flag indicating the line type, and an indentation level.
LINE_TYPES = [ :BLANK, :HEADING, :LIST, :PARAGRAPH, :RULE, :VERBATIM, ]
INFINITY = 9999
true if this line has been deleted from the list of lines
the number of leading spaces
A flag. For list lines, this is the type of the list
A prefix or parameter. For LIST lines, this is the text that introduced the list item (the label)
The indentation nesting level