anchor.diff:      environment.systemPackages =
         [ # Include zsh package
           pkgs.zsh
  -      ] ++ optional cfg.enableCompletion pkgs.nix-zsh-completions;
  +      ] ++ optional cfg.enableCompletion pkgs.nix-zsh-completions
  +        ++ optional cfg.enableSyntaxHighlighting pkgs.zsh-syntax-highlighting;
   
       environment.loginShell = mkDefault "${shell}/bin/zsh -l";
       environment.variables.SHELL = mkDefault "${shell}/bin/zsh";
  
positive.code:       ${optionalString cfg.enableCompletion "autoload -U compinit && compinit"}
        ${optionalString cfg.enableBashCompletion "autoload -U bashcompinit && bashcompinit"}
  
        # Read system-wide modifications.
        if test -f /etc/zshrc.local; then
          . /etc/zshrc.local
  
negative.code:       description = "Enable fzf keybinding for Ctrl-r history search.";
      };
  
      programs.zsh.enableSyntaxHighlighting = mkOption {
        type = types.bool;
        default = false;
        description = "Enable zsh-syntax-highlighting.";
      };
  
    };
  
    config = mkIf cfg.enable {
  