Did you check also how many years those references where published? Julia 1.0 was released in August 2018, any “reference” older than that should be taken with a pinch of salt.
Today you probably want to use eachmatch instead:
julia> eachmatch(r"[a-z]", "is a letter")
Base.RegexMatchIterator(r"[a-z]", "is a letter", false)
julia> collect(eachmatch(r"[a-z]", "is a letter"))
9-element Vector{RegexMatch}:
RegexMatch("i")
RegexMatch("s")
RegexMatch("a")
RegexMatch("l")
RegexMatch("e")
RegexMatch("t")
RegexMatch("t")
RegexMatch("e")
RegexMatch("r")