By default, links added with MarsEdit do not have any special behavior to cause them to open in a new window or tab. If you want a link in your blog post to open a new window when users click it, you can use MarsEdit’s custom formatting macros to achieve this.

1. Open a new post to get access to the Format menu.
2. Select Format -> Customize… (bottom of the menu).
3. Click the + button to make a new macro.
4. Name it something like “Link in New Window”
5. Enter this text for the opening markup:

   <a href="#askurl#" target="_blank">

6. Enter this text for the closing markup:

   </a>

7. Give it a keyboard shortcut if you like.

Now when you select Format -> Link in New Window, the generated HTML will cause the link to be opened in a window when clicked.