I was just digging through the styleguide, and spotted that at least in github/github where we fail the build if frozen_string_literal: true is not set, the suggested code won't actually run.

Should we update the guidance here? Or be more clear that large is the keyword here, and guide as to how to correctly opt out of frozen_string_literal (I don't actually know how to)

Avoid using String#+ when you need to construct large data chunks. Instead, use String#<<. Concatenation mutates the string instance in-place and is always faster than String#+, which creates a bunch of new string objects.

# good and also fast
html = ""
html << "<h1>Page title</h1>"

paragraphs.each do |paragraph|
  html << "<p>#{paragraph}</p>"
end