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diff --git a/doc/0/grammar/abnf.txt b/doc/0/grammar/abnf.txt
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+; Standards-compliant ABNF (RFC 5234, RFC 7405)
+
+; Compatible with: https://www.quut.com/abnfgen/
+
+; Unlike PEG, grammar rules in BNF are non-deterministic, which makes
+; it much more challenging to express our naive parse logic.  Whether
+; this ABNF file is truly accurate is difficult to assess.
+
+; The abnfgen(1) tool linked above can be used to generate arbitrary
+; strings matching the grammar in this file.  These can be fed into
+; the Zisp parser to reveal some potential bugs; either in the parser
+; itself, or this ABNF grammar.
+
+; Note that the tool may generate Zisp string literals with Unicode
+; escape sequences corresponding to surrogate code points; the parser
+; may reject these.  This is expected; it's difficult to rewrite this
+; ABNF grammar to exclude those Unicode values.
+
+; Other minor inaccuracies that aren't important include: This ABNF
+; forces line comments to be terminated with an LF character, when in
+; fact the end-of-file may also terminate them; the same applies to
+; hash-bang parsing which doesn't actually have to end in LF.  These
+; discrepancies won't make abnfgen(1) generate invalid strings; they
+; only make this ABNF more strict than the Zisp parser, so it won't
+; generate some strings that the parser would actually accept.
+
+
+Stream        = [ Unit *( Blank Unit ) ] *Blank [Trail]
+
+
+Unit          = *Blank Datum
+
+Blank         = HTAB / LF / %x0b / %x0c / CR / SP / Comment
+
+Trail         = SkipLine / SkipUnit / ";" "~" *Blank
+
+
+Datum         = BareString / SpecialStr / CladDatum / Rune / RuneStr
+              / RuneDotStr / RuneClad / LabelRef / LabelDef / HashStr
+              / HashDotStr / HashClad / QuoteExpr / JoinExpr
+
+Comment       = SkipLine LF / SkipUnit Blank
+
+SkipLine      = ";" [ SkipLStart *AnyButLF ]
+
+SkipUnit      = ";" "~" Unit
+
+SkipLStart    = %x00-09 / %x0b-7d / %x7f-ff ; any but LF or "~"
+
+AnyButLF      = %x00-09 / %x0b-ff
+
+
+BareString    = BareChar *( BareChar / Numeric )
+
+SpecialStr    = SpecStrChar *( SpecStrChar / BareChar )
+
+CladDatum     = "|" *( PipeStrChar / "\" StringEsc ) "|"
+              / DQUOTE *( QuotStrChar / "\" StringEsc ) DQUOTE
+              / "(" List ")"
+              / "[" List "]"
+              / "{" List "}"
+
+Rune          = "#" RuneName
+
+RuneStr       = "#" RuneName "\" BareString
+
+RuneDotStr    = "#" RuneName "\" SpecialStr
+
+RuneClad      = "#" RuneName CladDatum
+
+HashBang      = "#" "!" *( SP / HTAB ) HBLine LF
+
+LabelRef      = "#" "%" Label "%"
+
+LabelDef      = "#" "%" Label "=" Datum
+
+HashStr       = "#" "\" BareString
+
+HashDotStr    = "#" "\" SpecialStr
+
+HashClad      = "#" CladDatum
+
+QuoteExpr     = "'" Datum
+              / "`" Datum
+              / "," Datum
+
+JoinExpr      = Datum RJoinDatum
+              / LJoinDatum NoStartDot
+              / Datum ":" Datum
+              / NoEndDot "." Datum
+
+
+BareChar      = "!" / "$" / "%" / "&" / "*" / "/" / "<" / "=" / ">"
+              / "?" / "^" / "_" / "~" / ALPHA
+
+Numeric       = "+" / "-" / DIGIT
+
+SpecStrChar   = "." / ":" / Numeric
+
+PipeStrChar   = %x00-5b / %x5d-7b / %x7d-ff ; any but "|" or "\"
+
+QuotStrChar   = %x00-21 / %x23-5b / %x5d-ff ; any but DQUOTE or "\"
+
+StringEsc     = "\" / "|" / DQUOTE / *( HTAB / SP ) LF *( HTAB / SP )
+              / %s"a" / %s"b" / %s"t" / %s"n"
+              / %s"v" / %s"f" / %s"r" / %s"e"
+              / %s"x" *( 2HEXDIG ) ";"
+              / %s"u" ["0"] 1*5HEXDIG ";"
+              / %s"u" "1" "0" 4HEXDIG ";"
+
+List          = [ Unit *( Blank Unit ) ] *Blank [SkipUnit]
+
+
+RuneName      = ALPHA *5( ALPHA / DIGIT )
+
+Label         = 1*12( HEXDIG )
+
+HBLine        = 1*HBChar [ 1*( SP / HTAB ) *HBChar ]
+
+HBChar        = %x00-08 / %x0b-1f / %x21-ff ; any but HT, LF, SP
+
+
+RJoinDatum    = CladDatum / Rune / RuneStr / RuneDotStr / RuneClad
+              / LabelRef / LabelDef / HashStr / HashDotStr / HashClad
+              / QuoteExpr
+
+LJoinDatum    = CladDatum / RuneClad / LabelRef / HashClad
+
+NoStartDot    = BareString / CladDatum / Rune / RuneStr / RuneDotStr
+              / RuneClad / LabelRef / LabelDef / HashStr / HashDotStr
+              / HashClad / QuoteExpr
+
+NoEndDot      = BareString / Rune / RuneStr / RuneClad / LabelRef
+              / HashStr / HashClad
+
+
+;; Local Variables:
+;; eval: (flyspell-mode -1)
+;; End: