# Subsets of Markdown syntax structure
# expressed in parsing expression grammar (PEG) notation.
#
# Copyright 2025, Jonas Smedegaard <dr@jones.dk>
# SPDX-License-Identifier: GPL-3+

# Document
Markdown       <- ('---' NEWLINE MetaBlock* '---' NEWLINE)? Block*

# Block elements
Block          <- LinkDefinition
                / Header
                / List
                / Paragraph
Header         <- '#'+ SPACE* !NEWLINE Words? SPACE* NEWLINE
List           <- ([-*]+ / [[:digit:]]+ [).]) (_ (List / Words))? NEWLINE
LinkDefinition <- LinkLabel ':' _? Uri (_ LinkTitle)? NEWLINE
Paragraph      <- Words (HardBreak Words)* NEWLINE+

# Inline elements
Words          <- StyledWords
                / LinkedWords
                / AnnotatedWords
                / PlainWords
StyledWords    <- '**' Words '**'
                / '*' Words '*'
                / '_' Words '_'
LinkedWords    <- '[' Words ']' '(' ((Uri _)? LinkTitle / Uri) ')'
                / '[' Words ']' LinkLabel
                / LinkLabel
AnnotatedWords <- '[' Words ']' '{' KeyWords '}'
LinkLabel      <- '[' _? ![\[\]] PlainWords _? ']'
LinkTitle      <- '"' _? !'"' _? PlainWords _? '"'
                / "'" _? !"'" PlainWords _? "'"
                / "(" _? ![()] PlainWords _? ")"
KeyWords       <- KeyWord (_ KeyWord)*
PlainWords     <- PRINTABLES (_ PRINTABLES)*
KeyWord        <- Identifier / Class / Attribute / '-'
Identifier     <- '#' [[:alpha:]] [[:alnum:]]*
Class          <- '.' [[:alpha:]] [[:alnum:]]*
Attribute      <- [[:alpha:]] [[:alnum:]]* SPACE* = SPACE*
                  ('"' [[:alnum:]]+ '"' / [[:alnum:]]+)
Uri            <- '<' ![<>] PRINTABLES? '>'
                / ![<>] PRINTABLES
HardBreak      <- SPACE SPACE+ NEWLINE
_              <- SPACE+
                / SPACE? NEWLINE SPACE? SPACE? SPACE?

# Terminals
PRINTABLES     <- [[:graph:]]+
SPACE          <- ' '
NEWLINE        <- '\r\n'
                / '\n'
                / '\r'

# Semantic Markdown
# @see <https://source.jones.dk/semantic-markdown/about/>
BlockX         <- LinkDefinition
                / PrefixDefinition
                / Header
                / List
                / Paragraph
PrefixDefinition <- '{' CuriePrefix '}' ':' _? SemWord NEWLINE
KeyWordX         <- SemWord / Identifier / Class / Attribute / '-'
SemWord          <- SEMPREFIX ('<' ![<>] PRINTABLES '>' / Curie)
SEMPREFIX        <- [.=]

# RDF CURIE
# @see <https://www.w3.org/TR/rdfa-core/#s_curies>
Curie          <- (CuriePrefix? ':')? CurieReference
CuriePrefix    <- NCName
CurieReference <- (IriPathAbsolute / IriPathRootless / IriPathEmpty)
                  ('?' IriQuery)? ('#' IriFragment)?

# RFC3987 - Internationalized Resource Identifiers (IRIs)
# @see <https://tools.ietf.org/html/rfc3987>
IriPathAbsolute <- '/' (IriSegment ('/' IriSegment?)*)*
IriPathRootless <- IriSegment ('/' IriSegment?)*
IriPathEmpty    <- !IriPathChar
IriSegment      <- IriPathChar+
IriQuery        <- (IriPathChar / IriPrivate / '/' / '?')*
IriFragment     <- (IriPathChar / '/' / '?')*
IriPathChar     <- IriUnreserved / PctEncoded / SubDelims / ':' / '@'
IriUnreserved   <- [A-Za-z] / [0-9] / '-' / '.' / '_' / '~' / UcsChar
PctEncoded      <- '%' [0-9A-F] [0-9A-F]
SubDelims       <- '!' / '$' / '&' / "'" / '(' / ')'
                 / '*' / '+' / ',' / ';' / '='
UcsChar         <- [#xA0-#xD7FF] / [#xF900-#xFDCF] / [#xFDF0-#xFFEF]
                 / [#x10000-#x1FFFD] / [#x20000-#x2FFFD] / [#x30000-#x3FFFD]
                 / [#x40000-#x4FFFD] / [#x50000-#x5FFFD] / [#x60000-#x6FFFD]
                 / [#x70000-#x7FFFD] / [#x80000-#x8FFFD] / [#x90000-#x9FFFD]
                 / [#xA0000-#xAFFFD] / [#xB0000-#xBFFFD] / [#xC0000-#xCFFFD]
                 / [#xD0000-#xDFFFD] / [#xE1000-#xEFFFD]
IriPrivate      <- [#xE000-#xF8FF] / [#xF0000-#xFFFFD] / [#x100000-#x10FFFD]

# XML NCName
# @see <https://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName>
NCName <- !':' XMLName

# XML Name
# @see <https://www.w3.org/TR/REC-xml/#NT-Name>
XMLName          <- NameStartChar NameChar*
XMLNameChar      <- NameStartChar / "-" / "." / [0-9]
                  / #xB7 / [#x0300-#x036F] / [#x203F-#x2040]
XMLNAMESTARTCHAR <- ":" / "_" / [A-Z] / [a-z]
                  / [#xC0-#xD6] / [#xD8-#xF6]
                  / [#xF8-#x2FF] / [#x370-#x37D] / [#x37F-#x1FFF]
                  / [#x200C-#x200D] / [#x2070-#x218F] / [#x2C00-#x2FEF]
                  / [#x3001-#xD7FF] / [#xF900-#xFDCF] / [#xFDF0-#xFFFD]
                  / [#x10000-#xEFFFF]