chers

content: headline|board|paragraph\n*

headline: #text\n

paragraph: textcode\s*

board: =line ([1-9]\d*)\n

textcode: text|code

text: [^<>#\n]

code: fencode|linecode|linebranch

fencode: <line fen>
linecode: <line moves>
linebranch: <line line moves>

moves: move*
move: turn san san |
    turn san
turn: (\d)*... |
(\d)*.

<line fen>

<line 1. san san 2. san>
<line 2... san>
<line 3. san>

<line2 line 3... san>
<line2 4. san>