Because EPUB 3 is just a bunch of text files packaged into one file using zip, all text editor programs can be used to edit ePub 3. There are dozens of good text editors out there, including many which are smart about XHTML, CSS, and so on: Emacs, TextMate, Coda, Espresso, Notepad++, etc.
The complete EPUB 3.0 spec is available for all to read online at the
IDPF website.
A Foreign Resource is defined here:
http://idpf.org/epub/30/spec/epub30-...source-foreign
Foreign Resource = "A Publication Resource that is not a Core Media Type, ..."
The Core Media Types are listed in
a table (link).
You'll notice that video files are not listed, so they're Foreign Resources.
Therefore an example of using a Foreign Resource would be embedding a video of a cow walking up a hill in the sunshine.