A .gz, .bz2, .zst, .lz4, .xz or .lz file that holds no container is an archive of one file (ArchiveFormat.SingleStream).
Brotli (.br) has no magic number, so it is recognised by its file name only. A tar inside any of these is one archive. The
normative rules (detection order, the entry name, writing) are in archive.md ("Detection", "Single compressed files").
| Types | SingleStreamReader, SingleStreamWriter, ArchiveCompression |
| Detection | magic bytes first, then the first 512 bytes of the decompressed stream, then the file name |
| Entry name | the gzip header's file name, else the archive name without its compression extension, else data |
| Writing | exactly one regular file; levels through ArchiveCreateOptions.CompressionLevel |
| Limits | the whole decompressed stream is metered against MaxTotalSize and MaxExpansionRatio; the window (Zstandard) or dictionary (xz, lzip) a stream may declare is limited by MaxWindowSize, 8 MiB by default |