diff --git a/ext/misc/compress.c b/ext/misc/compress.c
index bf38d4c93c..6e7d8b6148 100644
--- a/ext/misc/compress.c
+++ b/ext/misc/compress.c
@@ -27,6 +27,21 @@ SQLITE_EXTENSION_INIT1
 ** seven bits per integer stored in the lower seven bits of each byte.
 ** More significant bits occur first.  The most significant bit (0x80)
 ** is a flag to indicate the end of the integer.
+**
+** This function, SQLAR, and ZIP all use the same "deflate" compression
+** algorithm, but each is subtly different:
+**
+**   *  ZIP uses raw deflate.
+**
+**   *  SQLAR uses the "zlib format" which is raw deflate with a two-byte
+**      algorithm-identification header and a four-byte checksum at the end.
+**
+**   *  This utility uses the "zlib format" like SQLAR, but adds the variable-
+**      length integer uncompressed size value at the beginning.
+**
+** This function might be extended in the future to support compression
+** formats other than deflate, by providing a different algorithm-id
+** mark following the variable-length integer size parameter.
 */
 static void compressFunc(
   sqlite3_context *context,
diff --git a/ext/misc/sqlar.c b/ext/misc/sqlar.c
index 17d0875938..e812d70c99 100644
--- a/ext/misc/sqlar.c
+++ b/ext/misc/sqlar.c
@@ -24,6 +24,14 @@ SQLITE_EXTENSION_INIT1
 ** If the type of X is SQLITE_BLOB, and compressing that blob using
 ** zlib utility function compress() yields a smaller blob, return the
 ** compressed blob. Otherwise, return a copy of X.
+**
+** SQLar uses the "zlib format" for compressed content.  The zlib format
+** contains a two-byte identification header and a four-byte checksum at
+** the end.  This is different from ZIP which uses the raw deflate format.
+**
+** Future enhancements to SQLar might add support for new compression formats.
+** If so, those new formats will be identified by alternative headers in the
+** compressed data.
 */
 static void sqlarCompressFunc(
   sqlite3_context *context,
diff --git a/manifest b/manifest
index 83bebcd068..88ec153d89 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C The\sshell\sdetects\sand\sopens\sZIP\sarchives\susing\sthe\szipfile\sextension.
-D 2018-01-06T21:46:01.434
+C Improved\scomments\son\sthe\ssqlar.c\sand\scompress.c\sextensions\sthat\sdescribe\nthe\sdifferences\sbetween\sthe\s"zlib\sformat"\sused\sby\sSQLAR,\sthe\sraw\sdeflate\nformat\sused\sby\sZIP,\sand\sthe\scustom\sformat\sused\sby\scompress.c.\s\sNo\schanges\nto\scode.
+D 2018-01-07T19:52:28.395
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 9536f61ce33172d4868707ecc10844a0abef9e2e775ad2434245a60406fd7e38
@@ -273,7 +273,7 @@ F ext/misc/btreeinfo.c d7fd9a2fe2fa33ba28488e2fce703ebecc759219ea9e0bb3b25478486
 F ext/misc/carray.c ed96c218ea940b85c9a274c4d9c59fe9491c299147a38a8bba537687bd6c6005
 F ext/misc/closure.c 0d2a038df8fbae7f19de42e7c7d71f2e4dc88704
 F ext/misc/completion.c 52c3f01523e3e387eb321b4739a89d1fe47cbe6025aa1f2d8d3685e9e365df0f
-F ext/misc/compress.c 122faa92d25033d6c3f07c39231de074ab3d2e83
+F ext/misc/compress.c dd4f8a6d0baccff3c694757db5b430f3bbd821d8686d1fc24df55cf9f035b189
 F ext/misc/csv.c 1a009b93650732e22334edc92459c4630b9fa703397cbb3c8ca279921a36ca11
 F ext/misc/dbdump.c 3509fa6b8932d04e932d6b6b827b6a82ca362781b8e8f3c77336f416793e215e
 F ext/misc/eval.c f971962e92ebb8b0a4e6b62949463ee454d88fa2
@@ -294,7 +294,7 @@ F ext/misc/sha1.c 0b9e9b855354910d3ca467bf39099d570e73db56
 F ext/misc/shathree.c 9e960ba50483214c6a7a4b1517f8d8cef799e9db381195178c3fd3ad207e10c0
 F ext/misc/showauth.c 732578f0fe4ce42d577e1c86dc89dd14a006ab52
 F ext/misc/spellfix.c 41cf26c6b89fcaa8798ae10ae64d39c1f1d9d6995152e545bd491c13058b8fac
-F ext/misc/sqlar.c d355cd8b6e7280d2f61d4737672922acb512a2ab1cee52399ffb88980476e31c
+F ext/misc/sqlar.c 57d5bc45cd5492208e451f697404be88f8612527d64c9d42f96b325b64983d74
 F ext/misc/stmt.c 6f16443abb3551e3f5813bb13ba19a30e7032830015b0f92fe0c0453045c0a11
 F ext/misc/totype.c 4a167594e791abeed95e0a8db028822b5e8fe512
 F ext/misc/unionvtab.c 2aa94902ea646e1aaf6c05eac944a14276cddd67735b2ad856030ffffbb6626c
@@ -1697,7 +1697,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 366469f5603367fabcadfc9ffe8cd1e23c649fea49a560178ca0858a16a7e4d1
-R 0f23134ec1d9b30706dc56d4edcd4f2b
+P 05c99eb8cefbb3366b6d4ae91e10aa0c82bdf5ea361f4b3375413783af9167ac
+R 1813bb08dedce0701d741a99a479782e
 U drh
-Z bf2fee513f6949a58534392bd37a9abf
+Z e662d2fceaa8f576c7d1d1fef9cf3ce7
diff --git a/manifest.uuid b/manifest.uuid
index 95d424063b..348cdf03c2 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-05c99eb8cefbb3366b6d4ae91e10aa0c82bdf5ea361f4b3375413783af9167ac
\ No newline at end of file
+c13415c5caf06eaa73086c500907451dfcdfd1354ac4a9ab63edb7255edbfa1b
\ No newline at end of file