You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: zsh-history-substring-search.rb
    path of file: ./repos/homebrew-core/Formula/z
    
    the code of the file until where you have to start completion: class ZshHistorySubstring
    
  def caveats
    <<~EOS
      To activate the history search, add the following at the end of your .zshrc:

        source #{HOMEBREW_PREFIX}/share/zsh-history-substring-search/zsh-history-substring-search.zsh

      You will also need to restart your terminal for this change to take effect.
    EOS
  end