Expand the comment on the definition of the Mem object to better explain the

meanings of the various flag bits.

FossilOrigin-Name: f2f0426035d4e0334be000a3eb62bbd7d61fdab7c2ef9ba13cfdf6482396dd13

manifest

@@ -1,5 +1,5 @@
-C Performance\soptimization\sin\sinitMemArray()\ssaves\sabout\s750K\scycles\swith\sonly\na\s4-byte\sincrease\sin\scode\ssize.
-D 2022-02-28T12:16:51.464
+C Expand\sthe\scomment\son\sthe\sdefinition\sof\sthe\sMem\sobject\sto\sbetter\sexplain\sthe\nmeanings\sof\sthe\svarious\sflag\sbits.
+D 2022-02-28T13:38:28.184
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -626,7 +626,7 @@ F src/util.c 602fe229f32a96ceccae4f40824129669582096f7c355f53dbac156c9fecef23
 F src/vacuum.c 6c38ddc52f0619865c91dae9c441d4d48bf3040d7dc1bc5b22da1e45547ed0b3
 F src/vdbe.c 4b969ebe6b61f87a90aebf817bc6ebda5075fe56987591091a9bf22556262484
 F src/vdbe.h a1d0e3b934e835e73edd146f2e7c4eadb711b5c9875c18159a57483fd78e550e
-F src/vdbeInt.h 2ff02995d153d30d362c99d27248b8a3bf825617a8e0d4d8d1e0231eca3bc4f7
+F src/vdbeInt.h d23573156379d0666dc3f04f0305ea50385ecaf7c788413a530a2523dbaf2c54
 F src/vdbeapi.c 1c80efbe51118bbecc7279023e75d18edcfa4b3dc441287e1718ee70ad594f58
 F src/vdbeaux.c 0f3ce77dabb1f897cc7d3812ed162ec5d31d2298d1aa41b606f8048a742c4b9e
 F src/vdbeblob.c 5e61ce31aca17db8fb60395407457a8c1c7fb471dde405e0cd675974611dcfcd
@@ -1944,9 +1944,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P bb520293d8c11518ba153b986662f081ebfd781d38eb624c509605fa9148f6e9 d74aa979530d4236f5900d2ef998b27065d352d7c18bcd822e5c8f1041a1a81c
-R 0cbe8ba68087a6c2d38d406f08a0fa0f
-T +closed d74aa979530d4236f5900d2ef998b27065d352d7c18bcd822e5c8f1041a1a81c
+P c3e9cd5e7430be0653a96a2097a695447549980e08cc8bd8d8097a50c954908e
+R 1afa8d37576887b173d9bf5fb651f41d
 U drh
-Z 9bc2a643cc2decfa66e7a766c34e11ae
+Z dd0779de4c53c5ff450355df311fc955
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-c3e9cd5e7430be0653a96a2097a695447549980e08cc8bd8d8097a50c954908e
+f2f0426035d4e0334be000a3eb62bbd7d61fdab7c2ef9ba13cfdf6482396dd13

src/vdbeInt.h

@@ -231,9 +231,44 @@ struct sqlite3_value {
 */
 #define MEMCELLSIZE offsetof(Mem,db)
 
-/* One or more of the following flags are set to indicate the validOK
+/* One or more of the following flags are set to indicate the
 ** representations of the value stored in the Mem struct.
 **
+**  *  MEM_Null                An SQL NULL value
+**
+**  *  MEM_Null|MEM_Zero       An SQL NULL with the virtual table
+**                             UPDATE no-change flag set
+**
+**  *  MEM_Null|MEM_Term|      An SQL NULL, but also contains a
+**        MEM_Subtype          pointer accessible using
+**                             sqlite3_value_pointer().
+**
+**  *  MEM_Null|MEM_Cleared    Special SQL NULL that compares non-equal
+**                             to other NULLs even using the IS operator.
+**
+**  *  MEM_Str                 A string, stored in Mem.z with
+**                             length Mem.n.  Zero-terminated if
+**                             MEM_Term is set.  This flag is
+**                             incompatible with MEM_Blob and
+**                             MEM_Null, but can appear with MEM_Int,
+**                             MEM_Real, and MEM_IntReal.
+**
+**  *  MEM_Blob                A blob, stored in Mem.z length Mem.n.
+**                             Incompatible with MEM_Str, MEM_Null,
+**                             MEM_Int, MEM_Real, and MEM_IntReal.
+**
+**  *  MEM_Blob|MEM_Zero       A blob in Mem.z of length Mem.n plus
+**                             MEM.u.i extra 0x00 bytes at the end.
+**                                       
+**  *  MEM_Int                 Integer stored in Mem.u.i.
+**
+**  *  MEM_Real                Real stored in Mem.u.r.
+**
+**  *  MEM_IntReal             Real stored as an integer in Mem.u.i.
+**
+**  *  MEM_Undefined           An undefined and/or uninitialized value.
+**                             Trying to use an Undefined value is an error.
+**
 ** If the MEM_Null flag is set, then the value is an SQL NULL value.
 ** For a pointer type created using sqlite3_bind_pointer() or
 ** sqlite3_result_pointer() the MEM_Term and MEM_Subtype flags are also set.