This is the complete Invisible XML grammar in XML. It is also available in iXML.
<ixml>
<comment>version 2023-05-09</comment>
<rule name='ixml'>
<alt>
<nonterminal name='s'/>
<option>
<nonterminal name='prolog'/>
</option>
<repeat1>
<nonterminal name='rule'/>
<sep>
<nonterminal name='RS'/>
</sep>
</repeat1>
<nonterminal name='s'/>
</alt>
</rule>
<rule mark='-' name='s'>
<alt>
<repeat0>
<alts>
<alt>
<nonterminal name='whitespace'/>
</alt>
<alt>
<nonterminal name='comment'/>
</alt>
</alts>
</repeat0>
</alt>
</rule>
<comment>Optional spacing</comment>
<rule mark='-' name='RS'>
<alt>
<repeat1>
<alts>
<alt>
<nonterminal name='whitespace'/>
</alt>
<alt>
<nonterminal name='comment'/>
</alt>
</alts>
</repeat1>
</alt>
</rule>
<comment>Required spacing</comment>
<rule mark='-' name='whitespace'>
<alt>
<inclusion tmark='-'>
<member code='Zs'/>
</inclusion>
</alt>
<alt>
<nonterminal name='tab'/>
</alt>
<alt>
<nonterminal name='lf'/>
</alt>
<alt>
<nonterminal name='cr'/>
</alt>
</rule>
<rule mark='-' name='tab'>
<alt>
<literal tmark='-' hex='9'/>
</alt>
</rule>
<rule mark='-' name='lf'>
<alt>
<literal tmark='-' hex='a'/>
</alt>
</rule>
<rule mark='-' name='cr'>
<alt>
<literal tmark='-' hex='d'/>
</alt>
</rule>
<rule name='comment'>
<alt>
<literal tmark='-' string='{'/>
<repeat0>
<alts>
<alt>
<nonterminal name='cchar'/>
</alt>
<alt>
<nonterminal name='comment'/>
</alt>
</alts>
</repeat0>
<literal tmark='-' string='}'/>
</alt>
</rule>
<rule mark='-' name='cchar'>
<alt>
<exclusion>
<member string='{}'/>
</exclusion>
</alt>
</rule>
<rule name='prolog'>
<alt>
<nonterminal name='version'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule name='version'>
<alt>
<literal tmark='-' string='ixml'/>
<nonterminal name='RS'/>
<literal tmark='-' string='version'/>
<nonterminal name='RS'/>
<nonterminal name='string'/>
<nonterminal name='s'/>
<literal tmark='-' string='.'/>
</alt>
</rule>
<rule name='rule'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='mark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<nonterminal name='name'/>
<nonterminal name='s'/>
<inclusion tmark='-'>
<member string='=:'/>
</inclusion>
<nonterminal name='s'/>
<nonterminal mark='-' name='alts'/>
<literal tmark='-' string='.'/>
</alt>
</rule>
<rule mark='@' name='mark'>
<alt>
<inclusion>
<member string='@^-'/>
</inclusion>
</alt>
</rule>
<rule name='alts'>
<alt>
<repeat1>
<nonterminal name='alt'/>
<sep>
<alts>
<alt>
<inclusion tmark='-'>
<member string=';|'/>
</inclusion>
<nonterminal name='s'/>
</alt>
</alts>
</sep>
</repeat1>
</alt>
</rule>
<rule name='alt'>
<alt>
<repeat0>
<nonterminal name='term'/>
<sep>
<alts>
<alt>
<literal tmark='-' string=','/>
<nonterminal name='s'/>
</alt>
</alts>
</sep>
</repeat0>
</alt>
</rule>
<rule mark='-' name='term'>
<alt>
<nonterminal name='factor'/>
</alt>
<alt>
<nonterminal name='option'/>
</alt>
<alt>
<nonterminal name='repeat0'/>
</alt>
<alt>
<nonterminal name='repeat1'/>
</alt>
</rule>
<rule mark='-' name='factor'>
<alt>
<nonterminal name='terminal'/>
</alt>
<alt>
<nonterminal name='nonterminal'/>
</alt>
<alt>
<nonterminal name='insertion'/>
</alt>
<alt>
<literal tmark='-' string='('/>
<nonterminal name='s'/>
<nonterminal name='alts'/>
<literal tmark='-' string=')'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule name='repeat0'>
<alt>
<nonterminal name='factor'/>
<alts>
<alt>
<literal tmark='-' string='*'/>
<nonterminal name='s'/>
</alt>
<alt>
<literal tmark='-' string='**'/>
<nonterminal name='s'/>
<nonterminal name='sep'/>
</alt>
</alts>
</alt>
</rule>
<rule name='repeat1'>
<alt>
<nonterminal name='factor'/>
<alts>
<alt>
<literal tmark='-' string='+'/>
<nonterminal name='s'/>
</alt>
<alt>
<literal tmark='-' string='++'/>
<nonterminal name='s'/>
<nonterminal name='sep'/>
</alt>
</alts>
</alt>
</rule>
<rule name='option'>
<alt>
<nonterminal name='factor'/>
<literal tmark='-' string='?'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule name='sep'>
<alt>
<nonterminal name='factor'/>
</alt>
</rule>
<rule name='nonterminal'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='mark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<nonterminal name='name'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule mark='@' name='name'>
<alt>
<nonterminal name='namestart'/>
<repeat0>
<nonterminal name='namefollower'/>
</repeat0>
</alt>
</rule>
<rule mark='-' name='namestart'>
<alt>
<inclusion>
<member string='_'/>
<member code='L'/>
</inclusion>
</alt>
</rule>
<rule mark='-' name='namefollower'>
<alt>
<nonterminal name='namestart'/>
</alt>
<alt>
<inclusion>
<member string='-.·‿⁀'/>
<member code='Nd'/>
<member code='Mn'/>
</inclusion>
</alt>
</rule>
<rule mark='-' name='terminal'>
<alt>
<nonterminal name='literal'/>
</alt>
<alt>
<nonterminal name='charset'/>
</alt>
</rule>
<rule name='literal'>
<alt>
<nonterminal name='quoted'/>
</alt>
<alt>
<nonterminal name='encoded'/>
</alt>
</rule>
<rule mark='-' name='quoted'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='tmark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<nonterminal name='string'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule mark='@' name='tmark'>
<alt>
<inclusion>
<member string='^-'/>
</inclusion>
</alt>
</rule>
<rule mark='@' name='string'>
<alt>
<literal tmark='-' string='"'/>
<repeat1>
<nonterminal name='dchar'/>
</repeat1>
<literal tmark='-' string='"'/>
</alt>
<alt>
<literal tmark='-' string='''/>
<repeat1>
<nonterminal name='schar'/>
</repeat1>
<literal tmark='-' string='''/>
</alt>
</rule>
<rule name='dchar'>
<alt>
<exclusion>
<member string='"'/>
<member from='#0' to='#1f'/>
<member from='#7f' to='#9f'/>
</exclusion>
</alt>
<alt>
<literal string='"'/>
<literal tmark='-' string='"'/>
</alt>
</rule>
<comment>all characters except controls; quotes must be doubled</comment>
<rule name='schar'>
<alt>
<exclusion>
<member string='''/>
<member from='#0' to='#1f'/>
<member from='#7f' to='#9f'/>
</exclusion>
</alt>
<alt>
<literal string='''/>
<literal tmark='-' string='''/>
</alt>
</rule>
<comment>all characters except controls; quotes must be doubled</comment>
<rule mark='-' name='encoded'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='tmark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<literal tmark='-' string='#'/>
<nonterminal name='hex'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule mark='@' name='hex'>
<alt>
<repeat1>
<inclusion>
<member from='0' to='9'/>
<member from='a' to='f'/>
<member from='A' to='F'/>
</inclusion>
</repeat1>
</alt>
</rule>
<rule mark='-' name='charset'>
<alt>
<nonterminal name='inclusion'/>
</alt>
<alt>
<nonterminal name='exclusion'/>
</alt>
</rule>
<rule name='inclusion'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='tmark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<nonterminal name='set'/>
</alt>
</rule>
<rule name='exclusion'>
<alt>
<option>
<alts>
<alt>
<nonterminal name='tmark'/>
<nonterminal name='s'/>
</alt>
</alts>
</option>
<literal tmark='-' string='~'/>
<nonterminal name='s'/>
<nonterminal name='set'/>
</alt>
</rule>
<rule mark='-' name='set'>
<alt>
<literal tmark='-' string='['/>
<nonterminal name='s'/>
<repeat0>
<alts>
<alt>
<nonterminal name='member'/>
<nonterminal name='s'/>
</alt>
</alts>
<sep>
<alts>
<alt>
<inclusion tmark='-'>
<member string=';|'/>
</inclusion>
<nonterminal name='s'/>
</alt>
</alts>
</sep>
</repeat0>
<literal tmark='-' string=']'/>
<nonterminal name='s'/>
</alt>
</rule>
<rule name='member'>
<alt>
<nonterminal name='string'/>
</alt>
<alt>
<literal tmark='-' string='#'/>
<nonterminal name='hex'/>
</alt>
<alt>
<nonterminal name='range'/>
</alt>
<alt>
<nonterminal name='class'/>
</alt>
</rule>
<rule mark='-' name='range'>
<alt>
<nonterminal name='from'/>
<nonterminal name='s'/>
<literal tmark='-' string='-'/>
<nonterminal name='s'/>
<nonterminal name='to'/>
</alt>
</rule>
<rule mark='@' name='from'>
<alt>
<nonterminal name='character'/>
</alt>
</rule>
<rule mark='@' name='to'>
<alt>
<nonterminal name='character'/>
</alt>
</rule>
<rule mark='-' name='character'>
<alt>
<literal tmark='-' string='"'/>
<nonterminal name='dchar'/>
<literal tmark='-' string='"'/>
</alt>
<alt>
<literal tmark='-' string='''/>
<nonterminal name='schar'/>
<literal tmark='-' string='''/>
</alt>
<alt>
<literal string='#'/>
<nonterminal name='hex'/>
</alt>
</rule>
<rule mark='-' name='class'>
<alt>
<nonterminal name='code'/>
</alt>
</rule>
<rule mark='@' name='code'>
<alt>
<nonterminal name='capital'/>
<option>
<nonterminal name='letter'/>
</option>
</alt>
</rule>
<rule mark='-' name='capital'>
<alt>
<inclusion>
<member from='A' to='Z'/>
</inclusion>
</alt>
</rule>
<rule mark='-' name='letter'>
<alt>
<inclusion>
<member from='A' to='Z'/>
<member from='a' to='z'/>
</inclusion>
</alt>
</rule>
<rule name='insertion'>
<alt>
<literal tmark='-' string='+'/>
<nonterminal name='s'/>
<alts>
<alt>
<nonterminal name='string'/>
</alt>
<alt>
<literal tmark='-' string='#'/>
<nonterminal name='hex'/>
</alt>
</alts>
<nonterminal name='s'/>
</alt>
</rule>
</ixml>