# 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       <- MetaBlock* Block*

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

# Inline elements
Words          <- StyledWords / LinkedWords / AnnotatedWords / PlainWords
StyledWords    <- '*' Words '*' / '**' Words '**' / '_' Words '_'
LinkedWords    <- '[' Words ']' '(' Uri ')'
                / '[' Words ']' '[' ![\[\]] LinkDefinitionKeyphrase ']'
                / '[' LinkDefinitionKeyphrase ']'
AnnotatedWords <- '[' Words ']' '{' ![{}] PlainWords '}'
PlainWords     <- PRINTABLES (SPACE PRINTABLES)*
Uri            <- '<' ![<>] PRINTABLES? '>' / ![<>] PRINTABLES
HardBreak      <- SPACE SPACE NEWLINE

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