; A CONL document is valid UTF-8, parsed line by line.
; An empty document is valid and represents "no value"
; which can be coerced to an empty map or list as appropriate.
;
; In accordance with tradition, a newline may be specified with
; either a newline (U+000A) or carriage return (U+000D), or both:
newline = "(\r|\n|\r\n)"

; Within a line, you can use tabs (U+0009) or spaces (U+0020) for blanks. Other
; unicode spaces (e.g. U+200B) are treated as any other character (so that
; parsing is not dependent on Unicode version or multibyte characters).
blank = "[ \t]"

; A comment begins with a ; (U+003B), and continues until the next newline.
; Any lines containing only blanks or only comments are ignored.
comment = ";[^\r\n]*"

; The indent level of a line is the string of tab and space characters at the start.
; Lines that contain no non-blank characters, or only blanks followed by a comment,
; are assumed to have the same indentation as the previous line.
;
; After a newline, outdents are generated until the indent level matches a preceding line.
; (one outdent per indent token generated since that line).
; After which, if the indent is longer than the previous line, an indent token is generated.
after_newline = outdent* indent?

; A quoted scalar begins with a double quote (U+0022) and ends with the same character. Quoted scalars provide escape sequences for hard to type characters
quoted_scalar = "/\"([^\\\\\"\\r\\n]|\\\\(\\\\|\"|t|r|n|\\{[09a-fA-F]{1,8}\\}))*\"/"
; The escape sequences are:
escape_sequences
  \\ = "\\" ; '\'
  \" = "\"" ; '"'
  \t = "\t" ; tab
  \r = "\r" ; carriage return
  \n = "\n" ; newline
  \{[09a-fA-F]{1,8}} ; unicode codepoint from U+0000 to U+10FFFF (unpaired surrogates are not allowed).

; A multiline scalar begins with three double quotes (U+0022) and ends at the
; next non-blank line at which the indent level is less than or equual to the
; current one. They may optionally contain a hint for syntax highlighters, but
; this is not part of the value. The hint may contain any character except ;/".
; As with values leading/trailing blanks are ignored but internal blanks are
; preserved.
; When parsing a multiline scalar:
; * leading and trailing whitespace and blanks are removed.
; * carraige returns are normalized so each line ends with just \n.
; * any blank lines that contain less indent than the first line of the value are treated as \n.
; * The ; character is treated as a literal semi-colon (not a comment).
multiline_scalar =  """
  """ blank? multiline_hint blank? comment? newline indent (.*) outdent
multiline_hint =  "/[^\";\r\n \t]([^\r\n;\"]*[^;\r\n \t])?/"

; A map key can contain any character except ;, =, \r, \n; and cannot start with
; a blank or quote, or end with a blank. It can also be a quoted scalar:
map_key
  = "/[^\";=\r\n \t]([^\r\n=;]*[^=;\r\n \t])?/"
  = quoted_scalar

; A list item is denoted by a single = sign.
list_item = "="

; A scalar value can either be a quoted scalar, a multiline scalar, or a sequence of any characters
; except ;, \r, \n. As with keys they cannot start with a blank or quote, or end with a blank.
scalar
  = "/[^\";\r\n \t]([^\r\n;]*[^;\r\n \t])?/"
  = quoted_scalar
  = multiline_scalar

; A map section consists of a series of key value pairs, separated by newlines.
map_section
  = map_key blank* "=" blank* scalar blank* comment? newline
  = map_key blank* "="? blank* comment? indent section outdent

list_section
  = list_item blank* scalar blank* comment? newline
  = list_item blank* comment? indent section outdent

section
  = map_section
  = list_section