htmlEntity method
Matches an HTML entity reference or numeric character reference (e.g. &,  ,  ).
Implementation
Parser<String> htmlEntity() => seq3(
char('&'),
[
seq2(
char('#'),
[
seq2(pattern('xX'), pattern('0-9a-fA-F').plus()),
digit().plus(),
].toChoiceParser(),
),
pattern('a-zA-Z0-9').plus(),
].toChoiceParser(),
char(';'),
).flatten(message: 'HTML entity expected');