minimal document structure

mindoc.rnc

start = html
html = element html { head, body }
head = element head { title | link+ }
link = element link { empty }
title = element title { text }

## 本文(body)はBlockのみではなくInlineも許す
body = element body { ( Block | Inline)+ }

## Blockは見出しのみ (hrはportability高いだけど必要性低いので基本セットからは削除、画像もまずはInlineで)
Block = ( h1 | h2 | h3 | h4 | h5 | h6 )

h1 = element h1 { Inline+ }
h2 = element h2 { Inline+ }
h3 = element h3 { Inline+ }
h4 = element h4 { Inline+ }
h5 = element h5 { Inline+ }
h6 = element h6 { Inline+ }

Embedded = ( img )
img = element img { empty }

## Inlineは改行・強調・リンク・ルビ・オブジェクト埋め込み（画像）とテキスト
Inline = ( br | em | a | ruby | ExtText | Embedded )

br = element br { empty }
em = element em { ExtText+ }
a  = element a { (Embedded | Inline)+ }
ruby = element ruby { (rb|rt|rp)+ }
rb = element rb { ExtText+ }
rt = element rt { ExtText+ }
rp = element rp { ExtText+ }

## ExtTextは外字も含めたテキスト
ExtText = ( text | external_char )

external_char = element external_char { empty }