(* Markdown EBNF Grammar *)

document = { block } ;

block = heading
      | horizontal_rule
      | code_block
      | quote_block
      | list
      | table
      | paragraph
      | blank_line ;

(* Headings *)
heading = atx_heading | setext_heading ;

atx_heading = "#" { "#" } [ " " ] inline_text newline ;

setext_heading = inline_text newline
                 ( ( "=" { "=" } ) | ( "-" { "-" } ) ) newline ;

(* Horizontal Rule *)
horizontal_rule = ( ( "*" [ " " ] "*" [ " " ] "*" { [ " " ] "*" } )
                  | ( "-" [ " " ] "-" [ " " ] "-" { [ " " ] "-" } )
                  | ( "_" [ " " ] "_" [ " " ] "_" { [ " " ] "_" } ) ) newline ;

(* Code Blocks *)
code_block = fenced_code_block | indented_code_block ;

fenced_code_block = "```" [ language_identifier ] newline
                    { code_line }
                    "```" newline ;

indented_code_block = { "    " code_line } ;

code_line = { character - newline } newline ;

language_identifier = { letter | digit | "-" | "+" } ;

(* Quote Blocks *)
quote_block = { ">" [ " " ] ( inline_text | "" ) newline } ;

(* Lists *)
list = unordered_list | ordered_list ;

unordered_list = { unordered_list_item } ;

ordered_list = { ordered_list_item } ;

unordered_list_item = [ " " { " " } ] ( "*" | "+" | "-" ) " " inline_text newline
                      { continuation_line } ;

ordered_list_item = [ " " { " " } ] digit { digit } "." " " inline_text newline
                    { continuation_line } ;

continuation_line = "    " inline_text newline ;

(* Tables *)
table = table_header table_separator { table_row } ;

table_header = "|" { table_cell "|" } newline ;

table_separator = "|" { table_align_spec "|" } newline ;

table_row = "|" { table_cell "|" } newline ;

table_cell = { character - ( "|" | newline ) } ;

table_align_spec = [ ":" ] "-" { "-" } [ ":" ] ;

(* Paragraphs *)
paragraph = inline_text { newline inline_text } newline ;

(* Inline Elements *)
inline_text = { inline_element } ;

inline_element = emphasis
               | strong
               | code_span
               | link
               | image
               | autolink
               | line_break
               | plain_text ;

emphasis = ( "*" non_asterisk_text "*" )
         | ( "_" non_underscore_text "_" ) ;

strong = ( "**" non_asterisk_text "**" )
       | ( "__" non_underscore_text "__" ) ;

code_span = "`" { "`" } non_backtick_text { "`" } "`" ;

link = "[" link_text "]" "(" link_url [ " " link_title ] ")" ;

image = "!" "[" alt_text "]" "(" image_url [ " " image_title ] ")" ;

autolink = "<" ( url | email ) ">" ;

line_break = "  " newline | "\\" newline ;

(* Text Content *)
plain_text = { character - special_char } ;

non_asterisk_text = { character - "*" } ;

non_underscore_text = { character - "_" } ;

non_backtick_text = { character - "`" } ;

link_text = { character - ( "[" | "]" ) } ;

alt_text = { character - ( "[" | "]" ) } ;

link_url = { character - ( "(" | ")" | " " ) } ;

image_url = { character - ( "(" | ")" | " " ) } ;

link_title = quote_string ;

image_title = quote_string ;

quote_string = ( '"' { character - '"' } '"' )
             | ( "'" { character - "'" } "'" ) ;

url = "http" [ "s" ] "://" { character - ">" } ;

email = { character - ( "@" | ">" ) } "@" { character - ">" } ;

(* Utilities *)
blank_line = newline ;

special_char = "*" | "_" | "`" | "[" | "]" | "(" | ")" | "#" | ">" | "|" | "!" | "\\" ;

newline = "\n" | "\r\n" ;

character = letter | digit | symbol | " " ;

letter = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m"
       | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
       | "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M"
       | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" ;

digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;

symbol = "!" | "@" | "#" | "$" | "%" | "^" | "&" | "*" | "(" | ")" | "-" | "_" | "="
       | "+" | "[" | "]" | "{" | "}" | "\\" | "|" | ";" | ":" | "'" | '"' | "," | "."
       | "<" | ">" | "/" | "?" | "~" | "`" ;