Is ":G" of ${name:s/l/r/:G} actually supported?

[Joachim Ansorg <mail@bashsupport.com>]

Hi,
I was reading about modifiers on page 
https://zsh.sourceforge.io/Doc/Release/Expansion.html#Modifiers, which says:

>   The forms ‘gs/l/r’ and ‘s/l/r/:G’ perform global substitution, i.e. substitute every occurrence of r for l. Note that the g or :G must appear in exactly the position shown.

But zsh 5.9 doesn't seem to support this:
  > value="/dir/subdir/file.csv"
  > echo ${value:s/dir/_/:G}
  zsh: unrecognized modifier `G'

Is ":G" actually supported or is the documentation outdated here?
I might be overlooking something very simple, though.

Thank you!
Joachim Ansorg
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