If builtin is true (not null and non-zero) that means that the function is builtin (is part of SQLite3). If builtin is false (zero or null) that means that the function was not "builtin" and was added by a user by some method (even though to a lay observer it appears to be part of the structure). Note that the concept of "builtin" is the same as the concept of "builtin" when buying a house. If the bathroom is "builtin" that means that it came with the house. If you add another bathroom, then that was not "builtin" when you bought the house, even though it may now form an integral part of the structure. Perhaps a more apropos description would be "written and maintained by the authors of SQLite3" although there is no reason why a "user" could not add their own functions that report as being "builtin" if they wanted to do so.