SQLite

**   *pnToken to the number of tokens in column iCol of the current row.
**
**   If parameter iCol is greater than or equal to the number of columns
**   in the table, SQLITE_RANGE is returned. Or, if an error occurs (e.g.
**   an OOM condition or IO error), an appropriate SQLite error code is 
**   returned.
**
**   This function may be quite inefficient if used with an FTS5 table
**   created with the "columnsize=0" option.
**
** xColumnText:
**   This function attempts to retrieve the text of column iCol of the
**   current document. If successful, (*pz) is set to point to a buffer
**   containing the text in utf-8 encoding, (*pn) is set to the size in bytes
**   (not characters) of the buffer and SQLITE_OK is returned. Otherwise,
**   if an error occurs, an SQLite error code is returned and the final values
**   of (*pz) and (*pn) are undefined.
**
** xPhraseCount:
**   Returns the number of phrases in the current query expression.
**
** xPhraseSize:
**   Returns the number of tokens in phrase iPhrase of the query. Phrases
**   are numbered starting from zero.
**
** xInstCount:
**   Set *pnInst to the total number of occurrences of all phrases within
**   the query within the current row. Return SQLITE_OK if successful, or
**   an error code (i.e. SQLITE_NOMEM) if an error occurs.
**
**   This API can be quite slow if used with an FTS5 table created with the
**   "detail=none" or "detail=column" option. If the FTS5 table is created 
**   with either "detail=none" or "detail=column" and "content=" option 
**   (i.e. if it is a contentless table), then this API always returns 0.
**
** xInst:
**   Query for the details of phrase match iIdx within the current row.
**   Phrase matches are numbered starting from zero, so the iIdx argument
**   should be greater than or equal to zero and smaller than the value
**   output by xInstCount().
**
**   Usually, output parameter *piPhrase is set to the phrase number, *piCol
**   to the column in which it occurs and *piOff the token offset of the
**   first token of the phrase. The exception is if the table was created
**   with the offsets=0 option specified. In this case *piOff is always
**   set to -1.
**
**   Returns SQLITE_OK if successful, or an error code (i.e. SQLITE_NOMEM) 
**   if an error occurs.
**
**   This API can be quite slow if used with an FTS5 table created with the
**   "detail=none" or "detail=column" option. 
**
** xRowid:
**   Returns the rowid of the current row.
**
** xTokenize:
**   Tokenize text using the tokenizer belonging to the FTS5 table.
**

**           pApi->xPhraseNext(pFts, &iter, &iCol, &iOff)
**       ){
**         // An instance of phrase iPhrase at offset iOff of column iCol
**       }
**
**   The Fts5PhraseIter structure is defined above. Applications should not
**   modify this structure directly - it should only be used as shown above
**   with the xPhraseFirst() and xPhraseNext() API methods (and by
**   xPhraseFirstColumn() and xPhraseNextColumn() as illustrated below).
**
**   This API can be quite slow if used with an FTS5 table created with the
**   "detail=none" or "detail=column" option. If the FTS5 table is created 
**   with either "detail=none" or "detail=column" and "content=" option 
**   (i.e. if it is a contentless table), then this API always iterates
**   through an empty set (all calls to xPhraseFirst() set iCol to -1).
**
** xPhraseNext()
**   See xPhraseFirst above.
**
** xPhraseFirstColumn()
**   This function and xPhraseNextColumn() are similar to the xPhraseFirst()
**   and xPhraseNext() APIs described above. The difference is that instead
**   of iterating through all instances of a phrase in the current row, these
**   APIs are used to iterate through the set of columns in the current row
**   that contain one or more instances of a specified phrase. For example:
**
**       Fts5PhraseIter iter;
**       int iCol;
**       for(pApi->xPhraseFirstColumn(pFts, iPhrase, &iter, &iCol);
**           iCol>=0;
**           pApi->xPhraseNextColumn(pFts, &iter, &iCol)
**       ){
**         // Column iCol contains at least one instance of phrase iPhrase
**       }
**
**   This API can be quite slow if used with an FTS5 table created with the
**   "detail=none" option. If the FTS5 table is created with either 
**   "detail=none" "content=" option (i.e. if it is a contentless table), 
**   then this API always iterates through an empty set (all calls to 
**   xPhraseFirstColumn() set iCol to -1).
**
**   The information accessed using this API and its companion
**   xPhraseFirstColumn() may also be obtained using xPhraseFirst/xPhraseNext
**   (or xInst/xInstCount). The chief advantage of this API is that it is
**   significantly more efficient than those alternatives when used with
**   "detail=column" tables.  
**
** xPhraseNextColumn()
**   See xPhraseFirstColumn above.
*/
struct Fts5ExtensionApi {
  int iVersion;                   /* Currently always set to 3 */

  void *(*xUserData)(Fts5Context*);

  int (*xColumnCount)(Fts5Context*);