The sqlite3_context structure
acts as a data container to pass information between the SQLite
library and a custom SQL function implementation. The structure
is created by the SQLite library and passed into the function
callbacks registered with sqlite3_create_function(). The callback
functions can extract the database connection or user-data
pointer from the context. The context is also used to pass back
an SQL result value or error condition.
An application should never create or destroy an sqlite3_context
structure.
The sqlite3_context structure
is opaque, and an application should never access any of the
data fields directly.