"and" "or" "and"

I'm not sure I understand what you are asking. The list of items comprises:

1. controls
2. menus and menu items
3. local or web-based content
4. scripts that modify the content Safari presents

Safari extensions let you add persistent items to Safari—controls, menus and menu items, local or web-based content, and scripts that modify the content Safari presents.
______________________

let you ~
1. add persistent items to Safari—controls
2. menus and menu items
3. local or web-based content
4. scripts that modify the content Safari presents

As far as I can understand what you are asking, no. The dash introduces the list.

Safari extensions let you add persistent items to Safari. These items are controls, etc. ...

Safari extensions let you add persistent items to Safari, such as:
- controls, and/or
-menus, and/or
-menu items, and or
- [local or web-based] content, and/or
- scrips,
that modify the content Safari presents.

thanks a lot~~

teechrSafari extensions let you add persistent items to Safari, such as:- controls, and/or-menus, and/or-menu items, and or- [local or web-based] content, and/or- scrips,that modify the content Safari presents.

I believe that "that modify the content Safari presents" is intended to apply only to scripts.

You may be right, GPY, given that last comma. However, I'm going out on a limb and letting the broader context override that interpretation.

teechrYou may be right, GPY, given that last comma. However, I'm going out on a limb and letting the broader context override that interpretation.

Actually, my interpretation was based on the broader context as much as on the punctuation. I think that, of those items, only scripts are able to "modify the content Safari presents", in the sense that I believe th

I disagree. I think any of those can modify the content.

teechrI disagree. I think any of those can modify the content.

Well, if nothing else, it seems odd to me that "local or web-based content" can "modify" content.