title: Sqlite source code reading. What the ids like F17025, U17032 are used for?
body: <p>In SQLite source code comments I see identificators like F17025, U17032, etc. </p>
  
  <p>sqlite3.c:</p>
  
  <pre><code>** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
  ** to enter a mutex. {F17024} If another thread is already within the mutex,
  ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
  ** SQLITE_BUSY. {F17025}  The sqlite3_mutex_try() interface returns SQLITE_OK
  ** upon successful entry.  {F17026} Mutexes created using
  ** SQLITE_MUTEX_RECURSIVE can be entered multiple times by the same thread.
  ** {F17027} In such cases the,
  </code></pre>
  
  <p>What they are used for? Probably there are some related docs?</p>