[1] DXL (JISX0130-1995) の構文定義に使われている BNF 変種について。

[2] JIS X 0130-1995 5. で定義されています。

[3]

• DEF = "::=" ;; 定義する
• OR = "|"
• option = "[" elements "]" ;; 0*1
• repetition = "{" elements "}" ;; 0*∞
• char-val = terminal-zero / terminal-one ;; 終端記号
• terminal-zero = "‘" 1*CHAR "’" ;; 水準 0
• terminal-one = "“" 1*CHAR "”" ;; 水準 1
• rule-name = rule-name-zero / rule-name-one ;; 非終端記号
• rule-name-zero = "<" 1*name-char ">"
• rule-name-one = "<<" 1*name-char ">>"

• rule = rule-name defined-as elements [FWS] EOD
• defined-as = [FWS] DEF [FWS]
• elements = [FWS] alternation [FWS]
• alternation = concatenation *(or-operator concatenation)
• or-operator = [FWS] OR [FWS]
• concatenation = element *(FWS element)
• element = rule-name / repetition / option / char-val

なお、水準 ("0" / "1") は規格の実装水準。