What does that .WARC file do?
The Web ARChive (WARC) archive format specifies a method for combining multiple digital resources into an aggregate archive file together with related information. The WARC format is a revision of the Internet Archive's ARC File Format that has traditionally been used to store "web crawls" as sequences of content blocks harvested from the World Wide Web. The WARC format generalizes the older format to better support the harvesting, access, and exchange needs of archiving organizations. Besides the primary content currently recorded, the revision accommodates related secondary content, such as assigned metadata, abbreviated duplicate detection events, and later-date transformations.
WARC is now recognised by most national library systems as the standard to follow for web archival.