diff --git a/manifest b/manifest
index abb0adcf47..fcb3dd292f 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\smissing\sVdbeCoverage()\sand\sVdbeCoverageNeverTaken()\smacros\sto\swindow.c.
-D 2018-06-27T20:24:59.489
+C Introduce\sthe\sconcept\sof\s"weak\sfallback"\sin\sthe\sparser.\s\sA\sweak\sfallback\nonly\soccurs\sif\sa\ssyntax\serror\swould\sresult\sotherwise.
+D 2018-06-28T03:38:49.164
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 0a3a6c81e6fcb969ff9106e882f0a08547014ba463cb6beca4c4efaecc924ee6
@@ -484,7 +484,7 @@ F src/os_win.c ac29c25cde4cfb4adacc59cdec4aa45698ca0e29164ea127859585ccd9faa354
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 1bb6a57fa0465296a4d6109a1a64610a0e7adde1f3acf3ef539a9d972908ce8f
 F src/pager.h c571b064df842ec8f2e90855dead9acf4cbe0d1b2c05afe0ef0d0145f7fd0388
-F src/parse.y 4661ac1382c18bc67e1680ea3e44a6835ebc770667fe32ee1720c38454304165
+F src/parse.y 9517b50d35e5e495a241541b49f5512b8e9bcbac3fbfdc659215555efa5c4f40
 F src/pcache.c 135ef0bc6fb2e3b7178d49ab5c9176254c8a691832c1bceb1156b2fbdd0869bd
 F src/pcache.h 072f94d29281cffd99e46c1539849f248c4b56ae7684c1f36626797fee375170
 F src/pcache1.c 716975564c15eb6679e97f734cec1bfd6c16ac3d4010f05f1f8e509fc7d19880
@@ -1662,8 +1662,8 @@ F tool/genfkey.README cf68fddd4643bbe3ff8e31b8b6d8b0a1b85e20f4
 F tool/genfkey.test 4196a8928b78f51d54ef58e99e99401ab2f0a7e5
 F tool/getlock.c f4c39b651370156cae979501a7b156bdba50e7ce
 F tool/kvtest-speed.sh 4761a9c4b3530907562314d7757995787f7aef8f
-F tool/lemon.c 33892e2a243865f73e6c6e7cecce3c6eb4bb95db4a3d9d86d146c8064feb92fd
-F tool/lempar.c bf7db78e7213f1d51516710483eab506fd52bf632c7abfb3e2e9b885c90c03e1
+F tool/lemon.c 93a321bd82b5c73191e95b2f27203048bf4d054fdab4a257b7a6c9541f31828d
+F tool/lempar.c c7371bad027fd516b7eaed36d03353972df35163672637cddd00f472889932f9
 F tool/libvers.c caafc3b689638a1d88d44bc5f526c2278760d9b9
 F tool/loadfts.c c3c64e4d5e90e8ba41159232c2189dba4be7b862
 F tool/logest.c 11346aa019e2e77a00902aa7d0cabd27bd2e8cca
@@ -1743,7 +1743,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 336de43a47e206fe7629072e5b8c80d4ede17ead8ef4dcf5d8da6833ff22d2f9
-R b7bd98ed0e43c8f2d4cb4f0d7b13d574
-U dan
-Z 38db85555459c758350756078d19d70e
+P 4383cb68a1241768ddb3f180f8cbb9ea1638f8806210b10aac1384b8a7ecdca2
+R 341c5aa0d73cc2ef03cecacf95853224
+T *branch * weak-fallback
+T *sym-weak-fallback *
+T -sym-exp-window-functions *
+U drh
+Z 196c50a9819aa6d1d98f4a403b164e6b
diff --git a/manifest.uuid b/manifest.uuid
index 76bb105dfe..6b74c95f01 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-4383cb68a1241768ddb3f180f8cbb9ea1638f8806210b10aac1384b8a7ecdca2
\ No newline at end of file
+c41d7079fb63831bd2f009b64cbf5a423e8119e6b841bfd9bd5a2d85fba3b142
\ No newline at end of file
diff --git a/src/parse.y b/src/parse.y
index b253480588..02989c28a2 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -216,6 +216,10 @@ columnname(A) ::= nm(A) typetoken(Y). {sqlite3AddColumn(pParse,&A,&Y);}
 %ifdef SQLITE_OMIT_COMPOUND_SELECT
   EXCEPT INTERSECT UNION
 %endif SQLITE_OMIT_COMPOUND_SELECT
+%ifndef SQLITE_OMIT_WINDOWFUNC
+  CURRENT FILTER FOLLOWING ?OVER PARTITION 
+  PRECEDING RANGE UNBOUNDED ?WINDOW 
+%endif SQLITE_OMIT_WINDOWFUNC
   REINDEX RENAME CTIME_KW IF
   .
 %wildcard ANY.
diff --git a/tool/lemon.c b/tool/lemon.c
index c2c9554c89..08d3f39eba 100644
--- a/tool/lemon.c
+++ b/tool/lemon.c
@@ -272,6 +272,7 @@ struct symbol {
                            ** union is the correct data type for this object */
   int bContent;            /* True if this symbol ever carries content - if
                            ** it is ever more than just syntax */
+  int bWeakFallback;       /* True for a weak fallback */
   /* The following fields are used by MULTITERMINALs only */
   int nsubsym;             /* Number of constituent symbols in the MULTI */
   struct symbol **subsym;  /* Array of constituent symbols */
@@ -2209,6 +2210,7 @@ enum e_state {
   WAITING_FOR_DESTRUCTOR_SYMBOL,
   WAITING_FOR_DATATYPE_SYMBOL,
   WAITING_FOR_FALLBACK_ID,
+  WAITING_FOR_WEAK_FALLBACK_ID,
   WAITING_FOR_WILDCARD_ID,
   WAITING_FOR_CLASS_ID,
   WAITING_FOR_CLASS_TOKEN,
@@ -2667,6 +2669,12 @@ to follow the previous rule.");
       }
       break;
     case WAITING_FOR_FALLBACK_ID:
+      if( x[0]=='?' ){
+        psp->state = WAITING_FOR_WEAK_FALLBACK_ID;
+        break;
+      }
+      /* Fall through */
+    case WAITING_FOR_WEAK_FALLBACK_ID:
       if( x[0]=='.' ){
         psp->state = WAITING_FOR_DECL_OR_RULE;
       }else if( !ISUPPER(x[0]) ){
@@ -2683,6 +2691,8 @@ to follow the previous rule.");
           psp->errorcnt++;
         }else{
           sp->fallback = psp->fallback;
+          sp->bWeakFallback = (psp->state==WAITING_FOR_WEAK_FALLBACK_ID);
+          psp->state = WAITING_FOR_FALLBACK_ID;
           psp->gp->has_fallback = 1;
         }
       }
@@ -4493,6 +4503,9 @@ void ReportTable(
       struct symbol *p = lemp->symbols[i];
       if( p->fallback==0 ){
         fprintf(out, "    0,  /* %10s => nothing */\n", p->name);
+      }else if( p->bWeakFallback ){
+        fprintf(out, " %4d,  /* %10s => %s (weak) */\n",
+          -p->fallback->index, p->name, p->fallback->name);
       }else{
         fprintf(out, "  %3d,  /* %10s => %s */\n", p->fallback->index,
           p->name, p->fallback->name);
@@ -5112,18 +5125,12 @@ struct symbol *Symbol_new(const char *x)
   if( sp==0 ){
     sp = (struct symbol *)calloc(1, sizeof(struct symbol) );
     MemoryCheck(sp);
+    memset(sp, 0, sizeof(*sp));
     sp->name = Strsafe(x);
     sp->type = ISUPPER(*x) ? TERMINAL : NONTERMINAL;
-    sp->rule = 0;
-    sp->fallback = 0;
     sp->prec = -1;
     sp->assoc = UNK;
-    sp->firstset = 0;
     sp->lambda = LEMON_FALSE;
-    sp->destructor = 0;
-    sp->destLineno = 0;
-    sp->datatype = 0;
-    sp->useCnt = 0;
     Symbol_insert(sp,sp->name);
   }
   sp->useCnt++;
diff --git a/tool/lempar.c b/tool/lempar.c
index 885cefe143..d625fcb0a4 100644
--- a/tool/lempar.c
+++ b/tool/lempar.c
@@ -90,6 +90,7 @@
 /************* Begin control #defines *****************************************/
 %%
 /************* End control #defines *******************************************/
+#define YY_NLOOKAHEAD ((int)(sizeof(yy_lookahead)/sizeof(yy_lookahead[0])))
 
 /* Define the yytestcase() macro to be a no-op if is not already defined
 ** otherwise.
@@ -172,7 +173,7 @@
 ** it appears.
 */
 #ifdef YYFALLBACK
-static const YYCODETYPE yyFallback[] = {
+static const int yyFallback[] = {
 %%
 };
 #endif /* YYFALLBACK */
@@ -519,24 +520,34 @@ static YYACTIONTYPE yy_find_shift_action(
   do{
     i = yy_shift_ofst[stateno];
     assert( i>=0 );
-    assert( i+YYNTOKEN<=(int)sizeof(yy_lookahead)/sizeof(yy_lookahead[0]) );
+    /*assert( i+YYNTOKEN<=YY_NLOOKAHEAD );*/
     assert( iLookAhead!=YYNOCODE );
     assert( iLookAhead < YYNTOKEN );
     i += iLookAhead;
-    if( yy_lookahead[i]!=iLookAhead ){
+    if( i>=YY_NLOOKAHEAD || yy_lookahead[i]!=iLookAhead
+    ){
 #ifdef YYFALLBACK
-      YYCODETYPE iFallback;            /* Fallback token */
+      int iFallback;            /* Fallback token */
       if( iLookAhead<sizeof(yyFallback)/sizeof(yyFallback[0])
-             && (iFallback = yyFallback[iLookAhead])!=0 ){
-#ifndef NDEBUG
-        if( yyTraceFILE ){
-          fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
-             yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
+       && (iFallback = yyFallback[iLookAhead])!=0
+      ){
+        if( iFallback<0 && yy_default[stateno]==YY_ERROR_ACTION ){
+          /* A weak fallback only happens if current lookahead is a
+          ** syntax error */
+          iFallback = -iFallback;
         }
+        if( iFallback>0 ){
+          /* A strong fallback happens regardless */
+#ifndef NDEBUG
+          if( yyTraceFILE ){
+            fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
+               yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
+          }
 #endif
-        assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
-        iLookAhead = iFallback;
-        continue;
+          assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
+          iLookAhead = iFallback;
+          continue;
+        }
       }
 #endif
 #ifdef YYWILDCARD