Double digit backreference is wrongly interpreted

[clupasq]

The regular expression ((((((((((.))))))))))\10 matches any two repeating characters.
It represents 10 capturing groups that point to the same character and a backreference to capturing group 10.

Regexper, however, sees the \10 as a backreference to group 1 followed by a literal "0": https://regexper.com/#%2F((((((((((.))))))))))%5C10%2F