TTL infinity


I have a templatized index schema file which allows me to set the TTL differently for each index.
"_ttl" : {
"enabled" : true,
"default" : "${TTL}",
"store" : "yes"

Sometimes I want to set this value to infinity.
But the doc is unclear on what the setting is for infinity.
Is it the common; -1 ??

BTW: I tried sending this from my email client, but it didn't appear
So I've sent it properly from the website
I sincerely apologize if it somehow shows up twice.

-- Chris