Definition(en): These files may be produced by saving a web page in various versions of Apple's Safari Web Browser. The file is a type of Binary Property List (https://en.wikipedia.org/wiki/Property_list) and will contain the html content of the page, plus any page attachments. With further research and a better understanding of the format it may be possible to create a PRONOM identification signature, based on the 'bplist' magic number and further identifiers specific to the Apple Safari Webarchive format.