This element is a child of xfj:document or xfj:overlay. Please refer to these topics before reading.
The xfj:external-content element points to the actual document included via xfj:document or xfj:overlay. The src attribute supports a file URL (local or remote), an HTTP address or a Base64 blob. Also, it's allowed to omit the url(...) wrapper and just write: src="file_url".
Note: The file_url must be accessible by the XF Ultrascale 2011 Server, for example a relative/absolute file path on the server or a HTTP address. The Base64 bytes of the actual file can also be included, provided that the correct syntax is used. In this case, the file_url should be of the following form:
data:,BASE64BLOB