pub fn htm_tag(s: &str) -> Option<&str> {
let mut iter = s.char_indices();
if let Some((pos, c)) = iter.next()
&& c.is_ascii_alphabetic()
{
let begin = pos;
let mut end = s.len();
for (pos, c) in iter {
if !c.is_alphanumeric() {
end = pos;
break;
}
}
return Some(&s[begin..end]);
}
None
}