Complex sentence: Mac OS was the first to implement Desktop Search with its AppleSearch search engine, allowing users to fully search all documents within their Macintosh computer, including file format types, meta-data on those files, and content within the files.
Split into simpler sentences: Mac OS was the first to fully implement Desktop Search, it allowed users to fully search all documents with in their Macintosh computer. This means file format types, meta-data on those file formats and the content within the files.