regexp curly braces do not work

Hyunho Cho <[email protected]>
Newsgroups gmane.comp.gnu.m4.bugs
Message-ID <CAMMw470U8ni6d_JoRi33OPXhXKkLGQGeTAjj8vMb6qfpoUEjEw@mail.gmail.com>
m4 (GNU M4) 1.4.18
Operating System: Ubuntu 20.04 LTS
Kernel: Linux 5.4.0-33-generic
Architecture: x86-64


sh$ m4 <<\@
patsubst(`hello', `ll', `XX')
patsubst(`hello', `l+', `XX')
patsubst(`hello', `l\{2\}', `XX')
patsubst(`hello', `l{2}', `XX')
@
heXXo
heXXo
hello
hello
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