Index: src/backlink.c
==================================================================
--- src/backlink.c
+++ src/backlink.c
@@ -179,11 +179,12 @@
   rid = db_int(0, "SELECT rid FROM tagxref WHERE tagid=%d"
                   " ORDER BY mtime DESC LIMIT 1", tagid);
   if( rid==0 ) return;
   pWiki = manifest_get(rid, CFTYPE_WIKI, 0);
   if( pWiki ){
-    backlink_extract(pWiki->zWiki, pWiki->zMimetype, tagid, BKLNK_WIKI,
+    int mimetype = parse_mimetype( pWiki->zMimetype );
+    backlink_extract(pWiki->zWiki, mimetype, tagid, BKLNK_WIKI,
                      pWiki->rDate, 1);
     manifest_destroy(pWiki);
   }
 }
 
@@ -295,17 +296,28 @@
   markdown(&out, &in, &html_renderer);
   blob_reset(&out);
   blob_reset(&in);
 }
 
+/*
+** Transform mimetype string into an integer code.
+** NOTE: In the sake of compatability empty string is parsed as MT_UNKNOWN;
+**       it is yet unclear whether it can safely be changed to MT_NONE.
+*/
+int parse_mimetype(const char* zMimetype){
+  if( zMimetype==0 ) return MT_NONE;
+  if( strstr(zMimetype,"wiki")!=0 )     return MT_WIKI;
+  if( strstr(zMimetype,"markdown")!=0 ) return MT_MARKDOWN;
+  return MT_UNKNOWN;
+}
 /*
 ** Parse text looking for hyperlinks.  Insert references into the
 ** BACKLINK table.
 */
 void backlink_extract(
   char *zSrc,            /* Input text from which links are extracted */
-  const char *zMimetype, /* Mimetype of input.  NULL means fossil-wiki */
+  int mimetype,          /* Mimetype of input. MT_NONE works as MT_WIKI */
   int srcid,             /* srcid for the source document */
   int srctype,           /* One of BKLNK_*.  0=comment 1=ticket 2=wiki */
   double mtime,          /* mtime field for new BACKLINK table entries */
   int replaceFlag        /* True to overwrite prior BACKLINK entries */
 ){
@@ -314,15 +326,16 @@
     db_multi_exec("DELETE FROM backlink WHERE srctype=%d AND srcid=%d",
                   srctype, srcid);
   }
   bklnk.srcid = srcid;
   assert( ValidBklnk(srctype) );
+  assert( ValidMTC(mimetype) );
   bklnk.srctype = srctype;
   bklnk.mtime = mtime;
-  if( zMimetype==0 || strstr(zMimetype,"wiki")!=0 ){
+  if( mimetype==MT_NONE || mimetype==MT_WIKI ){
     wiki_extract_links(zSrc, &bklnk, srctype==BKLNK_COMMENT ? WIKI_INLINE : 0);
-  }else if( strstr(zMimetype,"markdown")!=0 ){
+  }else if( mimetype==MT_MARKDOWN ){
     markdown_extract_links(zSrc, &bklnk);
   }
 }
 
 /*
@@ -340,10 +353,11 @@
 **    --mimetype TYPE         Use an alternative mimetype.
 */
 void test_backlinks_cmd(void){
   const char *zMTime = find_option("mtime",0,1);
   const char *zMimetype = find_option("mimetype",0,1);
+  const int mimetype = parse_mimetype(zMimetype);
   Blob in;
   int srcid;
   int srctype;
   double mtime;
 
@@ -371,11 +385,11 @@
     " ' srcid='||quote(new.srcid)||"
     " ' mtime='||datetime(new.mtime));\n"
     "  SELECT raise(ignore);\n"
     "END;"
   );
-  backlink_extract(blob_str(&in),zMimetype,srcid,srctype,mtime,0);
+  backlink_extract(blob_str(&in),mimetype,srcid,srctype,mtime,0);
   blob_reset(&in);
 }
 
 
 /*

Index: src/manifest.c
==================================================================
--- src/manifest.c
+++ src/manifest.c
@@ -2395,11 +2395,11 @@
         rid, p->zUser, p->zComment,
         TAG_BGCOLOR, rid,
         TAG_USER, rid,
         TAG_COMMENT, rid, p->rDate
       );
-      backlink_extract(zCom, 0, rid, BKLNK_COMMENT, p->rDate, 1);
+      backlink_extract(zCom, MT_NONE, rid, BKLNK_COMMENT, p->rDate, 1);
       fossil_free(zCom);
 
       /* If this is a delta-manifest, record the fact that this repository
       ** contains delta manifests, to free the "commit" logic to generate
       ** new delta manifests.
@@ -2853,11 +2853,12 @@
         p->rDate, rid, p->zUser, zFType, zTitle
       );
       fossil_free(zTitle);
     }
     if( p->zWiki[0] ){
-      backlink_extract(p->zWiki, p->zMimetype, rid, BKLNK_FORUM, p->rDate, 1);
+      int mimetype = parse_mimetype(p->zMimetype);
+      backlink_extract(p->zWiki, mimetype, rid, BKLNK_FORUM, p->rDate, 1);
     }
   }
 
   db_end_transaction(0);
   if( permitHooks ){

Index: src/schema.c
==================================================================
--- src/schema.c
+++ src/schema.c
@@ -489,10 +489,21 @@
 # define BKLNK_EVENT      3   /* Technote */
 # define BKLNK_FORUM      4   /* Forum post */
 # define ValidBklnk(X)   (X>=0 && X<=4)  /* True if backlink.srctype is valid */
 #endif
 
+/*
+** Allowed values for MIMEtype codes
+*/
+#if INTERFACE
+# define MT_NONE       0   /* unspecified */
+# define MT_WIKI       1   /* Wiki */
+# define MT_MARKDOWN   2   /* Markdonw */
+# define MT_UNKNOWN    3   /* unknown  */
+# define ValidMTC(X)  ((X)>=0 && (X)<=3)  /* True if MIMEtype code is valid */
+#endif
+
 /*
 ** Predefined tagid values
 */
 #if INTERFACE
 # define TAG_BGCOLOR    1     /* Set the background color for display */

Index: src/tag.c
==================================================================
--- src/tag.c
+++ src/tag.c
@@ -220,11 +220,11 @@
   if( zCol ){
     db_multi_exec("UPDATE event SET \"%w\"=%Q WHERE objid=%d",
                   zCol, zValue, rid);
     if( tagid==TAG_COMMENT ){
       char *zCopy = mprintf("%s", zValue);
-      backlink_extract(zCopy, 0, rid, BKLNK_COMMENT, mtime, 1);
+      backlink_extract(zCopy, MT_NONE, rid, BKLNK_COMMENT, mtime, 1);
       free(zCopy);
     }
   }
   if( tagid==TAG_DATE ){
     db_multi_exec("UPDATE event "

Index: src/tkt.c
==================================================================
--- src/tkt.c
+++ src/tkt.c
@@ -40,10 +40,13 @@
 static u8 haveTicket = 0;        /* True if the TICKET table exists */
 static u8 haveTicketCTime = 0;   /* True if TICKET.TKT_CTIME exists */
 static u8 haveTicketChng = 0;    /* True if the TICKETCHNG table exists */
 static u8 haveTicketChngRid = 0; /* True if TICKETCHNG.TKT_RID exists */
 static u8 haveTicketChngUser = 0;/* True if TICKETCHNG.TKT_USER exists */
+static u8 useTicketGenMt = 0;    /* use generated TICKET.MIMETYPE */
+static u8 useTicketChngGenMt = 0;/* use generated TICKETCHNG.MIMETYPE */
+
 
 /*
 ** Compare two entries in aField[] for sorting purposes
 */
 static int nameCmpr(const void *a, const void *b){
@@ -70,11 +73,11 @@
 ** The haveTicket and haveTicketChng variables are set to 1 if the TICKET and
 ** TICKETCHANGE tables exist, respectively.
 */
 static void getAllTicketFields(void){
   Stmt q;
-  int i;
+  int i, noRegularMimetype;
   static int once = 0;
   if( once ) return;
   once = 1;
   db_prepare(&q, "PRAGMA table_info(ticket)");
   while( db_step(&q)==SQLITE_ROW ){
@@ -115,13 +118,25 @@
     aField[nField].mUsed = USEDBY_TICKETCHNG;
     nField++;
   }
   db_finalize(&q);
   qsort(aField, nField, sizeof(aField[0]), nameCmpr);
+  noRegularMimetype = 1;
   for(i=0; i<nField; i++){
     aField[i].zValue = "";
     aField[i].zAppend = 0;
+    if( strcmp(aField[i].zName,"mimetype")==0 ){
+      noRegularMimetype = 0;
+    }
+  }
+  if( noRegularMimetype ){ /* check for generated "mimetype" columns */
+    useTicketGenMt = db_exists(
+      "SELECT 1 FROM pragma_table_xinfo('ticket') "
+      "WHERE name = 'mimetype'");
+    useTicketChngGenMt = db_exists(
+      "SELECT 1 FROM pragma_table_xinfo('ticketchng') "
+      "WHERE name = 'mimetype'");
   }
 }
 
 /*
 ** Query the database for all TICKET fields for the specific
@@ -194,18 +209,18 @@
 **
 ** Parameter rid is the recordID for the ticket artifact in the BLOB table.
 **
 ** Return the new rowid of the TICKET table entry.
 */
-static int ticket_insert(const Manifest *p, int rid, int tktid){
+static int ticket_insert(const Manifest *p, const int rid, int tktid){
   Blob sql1; /* update or replace TICKET ... */
   Blob sql2; /* list of TICKETCHNG's fields that are in the manifest */
   Blob sql3; /* list of values which correspond to the previous list */
   Stmt q;
   int i, j;
   char *aUsed;
-  const char *zMimetype = 0;
+  int mimetype_tkt = MT_NONE, mimetype_tktchng = MT_NONE;
 
   if( tktid==0 ){
     db_multi_exec("INSERT INTO ticket(tkt_uuid, tkt_mtime) "
                   "VALUES(%Q, 0)", p->zTicketUuid);
     tktid = db_last_insert_rowid();
@@ -236,27 +251,30 @@
     if( aField[j].mUsed & USEDBY_TICKETCHNG ){
       blob_append_sql(&sql2, ",\"%w\"", zBaseName);
       blob_append_sql(&sql3, ",%Q", p->aField[i].zValue);
     }
     if( strcmp(zBaseName,"mimetype")==0 ){
-      zMimetype = p->aField[i].zValue;
-    }
-  }
-  if( rid>0 ){
-    for(i=0; i<p->nField; i++){
-      const char *zName = p->aField[i].zName;
-      const char *zBaseName = zName[0]=='+' ? zName+1 : zName;
-      j = fieldId(zBaseName);
-      if( j<0 ) continue;
-      backlink_extract(p->aField[i].zValue, zMimetype, rid, BKLNK_TICKET,
-                       p->rDate, i==0);
+      const char *zMimetype = p->aField[i].zValue;
+      /* "mimetype" is a regular column => these two flags must be 0 */
+      assert(!useTicketGenMt);
+      assert(!useTicketChngGenMt);
+      mimetype_tkt = mimetype_tktchng = parse_mimetype( zMimetype );
     }
   }
   blob_append_sql(&sql1, " WHERE tkt_id=%d", tktid);
+  if( useTicketGenMt ){
+    blob_append_literal(&sql1, " RETURNING mimetype");
+  }
   db_prepare(&q, "%s", blob_sql_text(&sql1));
   db_bind_double(&q, ":mtime", p->rDate);
   db_step(&q);
+  if( useTicketGenMt ){
+    mimetype_tkt = parse_mimetype( db_column_text(&q,0) );
+    if( !useTicketChngGenMt ){
+      mimetype_tktchng = mimetype_tkt;
+    }
+  }
   db_finalize(&q);
   blob_reset(&sql1);
   if( blob_size(&sql2)>0 || haveTicketChngRid || haveTicketChngUser ){
     int fromTkt = 0;
     if( haveTicketChngRid ){
@@ -278,25 +296,55 @@
         blob_append_sql(&sql3, ",\"%w\"", z);
       }
     }
     if( fromTkt ){
       db_prepare(&q, "INSERT INTO ticketchng(tkt_id,tkt_mtime%s)"
-                     "SELECT %d,:mtime%s FROM ticket WHERE tkt_id=%d",
+                     "SELECT %d,:mtime%s FROM ticket WHERE tkt_id=%d%s",
                      blob_sql_text(&sql2), tktid,
-                     blob_sql_text(&sql3), tktid);
+                     blob_sql_text(&sql3), tktid,
+                     useTicketChngGenMt ? " RETURNING mimetype" : "");
     }else{
       db_prepare(&q, "INSERT INTO ticketchng(tkt_id,tkt_mtime%s)"
-                     "VALUES(%d,:mtime%s)",
-                     blob_sql_text(&sql2), tktid, blob_sql_text(&sql3));
+                     "VALUES(%d,:mtime%s)%s",
+                     blob_sql_text(&sql2), tktid, blob_sql_text(&sql3),
+                     useTicketChngGenMt ? " RETURNING mimetype" : "");
     }
     db_bind_double(&q, ":mtime", p->rDate);
     db_step(&q);
+    if( useTicketChngGenMt ){
+      mimetype_tktchng = parse_mimetype( db_column_text(&q, 0) );
+      /* substitute NULL with a value generated within another table */
+      if( !useTicketGenMt ){
+        mimetype_tkt = mimetype_tktchng;
+      }else if( mimetype_tktchng==MT_NONE ){
+        mimetype_tktchng = mimetype_tkt;
+      }else if( mimetype_tkt==MT_NONE ){
+        mimetype_tkt = mimetype_tktchng;
+      }
+    }
     db_finalize(&q);
   }
   blob_reset(&sql2);
   blob_reset(&sql3);
   fossil_free(aUsed);
+  if( rid>0 ){                   /* extract backlinks */
+    int bReplace = 1, mimetype;
+    for(i=0; i<p->nField; i++){
+      const char *zName = p->aField[i].zName;
+      const char *zBaseName = zName[0]=='+' ? zName+1 : zName;
+      j = fieldId(zBaseName);
+      if( j<0 ) continue;
+      if( aField[j].mUsed & USEDBY_TICKETCHNG ){
+        mimetype = mimetype_tktchng;
+      }else{
+        mimetype = mimetype_tkt;
+      }
+      backlink_extract(p->aField[i].zValue, mimetype, rid, BKLNK_TICKET,
+                       p->rDate, bReplace);
+      bReplace = 0;
+    }
+  }
   return tktid;
 }
 
 /*
 ** Returns non-zero if moderation is required for ticket changes and ticket