+ The default is to use the constant-memory lazy way, when possible
+ (see below).
+
+ However, with FTS_LOGICAL (when following symlinks, e.g., chown -L)
+ using lazy cycle detection is inadequate. For example, traversing
+ a directory containing a symbolic link to a peer directory, it is
+ possible to encounter the same directory twice even though there
+ is no cycle:
+ dir
+ ...
+ slink -> dir
+ So, when FTS_LOGICAL is selected, we have to use a different
+ mode of cycle detection: FTS_TIGHT_CYCLE_CHECK. */