+The 'fmt' argument is passed directly as the 'fmt' parameter of
+man:vasprintf(3), as well as:
+
+For `tracelog()`::
+ The optional parameters following 'fmt'.
+
+For `vtracelog()`::
+ The 'ap' parameter as the 'ap' parameter of man:vasprintf(3)
+ (`va_list` type).
+
+The purpose of `tracelog()` and `vtracelog()` is to ease the migration
+from logging to tracing.