Opening external links in a new window can be useful, but adding target="_blank" can be a real chore. Not only that, but if you are trying to validate the page to XHTML strict then the target attribute will cause errors to appear as it is not defined in XHTML.
Yesterday I talked about using the Flex Script element to run code within the mxml file, you can also use the source attribute of the Script element to reference external files. To create an external script file FlashDevelop go to the File->New and select Blank Document. You can also do this by pressing Ctrl+N.