Adding Embed Whitelist Items
Files you'll want to poke include:
In the code hook, most sites can be added to
%host_path_match with a simple regular expression to test that the URL is in the expected format. The second argument is 1 or 0 depending on whether the site supports https connections or not - you should test this.
In the test suite, you'll want to add a simple check to make sure the URL you were given as a test case passes your check to be allowed on the site. See Dev Testing for more information about setting up and running the automated tests.