Hi Ivan,
The code handles group name was added later. So "historically" those cases
trigger "unknow look-behind group" when the first character after "<" is not
"=" or "?". With the addition of the group name support, it's actually
hard to
say which one is more accurate, incorrect group name
Hello!
Capturing group name can be used in a regular expression in two
contexts: When introducing a group (?...) or when referring it
\k.
If the name is invalid (i.e. does not start with a Latin letter, or
contains wrong chars) then we may see different error messages, some of
which look
