Minor clarification of effective level calculation

Doc/lib/liblogging.tex

@@ -334,6 +334,20 @@ created, the level is set to \constant{NOTSET} (which causes all messages
 to be processed when the logger is the root logger, or delegation to the
 parent when the logger is a non-root logger). Note that the root logger
 is created with level \constant{WARNING}.
+
+The term "delegation to the parent" means that if a logger has a level
+of NOTSET, its chain of ancestor loggers is traversed until either an
+ancestor with a level other than NOTSET is found, or the root is
+reached.
+
+If an ancestor is found with a level other than NOTSET, then that
+ancestor's level is treated as the effective level of the logger where
+the ancestor search began, and is used to determine how a logging
+event is handled.
+
+If the root is reached, and it has a level of NOTSET, then all
+messages will be processed. Otherwise, the root's level will be used
+as the effective level.
 \end{methoddesc}
 
 \begin{methoddesc}{isEnabledFor}{lvl}