changequote oddity

Jack Andrews <[email protected]> Thu, 20 Jul 2017 19:29:39 +1000
Newsgroups gmane.comp.gnu.m4.general
Message-ID <CAJvHTNwvA15kp9M2anFqDhop76VU6PcxqPuSBesEvTdEbKEP5Q@mail.gmail.com>
new to m4, but i can't explain why the last ` in this file appears to quote
the rest of file?
note the last changequote()

i got the define from stackoverflow...

$ cat f
define(`ticks',changequote([,])[changequote([,])```changequote(`,')]changequote(`,'))dnl
changequote(<,>)dnl
expandticks (ticks)
expandticks (`ticks)
'
$ m4 f
expandticks (```)
expandticks (ticks)