Syntax guide traefik rules parsing? " vs ' vs ` in HostSNI?

I can't find a page that details whats legal syntax for traefik rules. Today I discovered that HostSNI only accepts a `` enclosed strings for example - a style of string quoting i've seen in various samples but not seen explained, and Host & HostRegEx seem to accept "" and '' enclosed strings as one would expect.

https://docs.traefik.io/routing/routers/#rule

Backticks or Quotes?

To set the value of a rule, use backticks ` or escaped double-quotes \" .

Single quotes ' are not accepted as values are Golang's String Literals.