Got an "invalid repeat count" error from regexp

The following error appeared in mysql:

Got error 'invalid repetition count(s)' from regexp

My request:

SELECT * FROM table WHERE some_text_field REGEXP"[A-Za-z0-9]{256}"

But when I replace REGEXP"[A-Za-z0-9]{256}"with REGEXP"[A-Za-z0-9]{255}", and below there is no error.

Is there a character limit in REGEXP? Why doesn't it work when I use 256 or higher, but it works when I replace it with 255 or lower?

I examined this, the Mysql exception exception for Regex , but it is not very informative why the error occurs.