1 files changed, 21 insertions, 2 deletions
diff --git a/pod/perlguts.pod b/pod/perlguts.pod
index 105e8171d2..4fe07983da 100644
--- a/pod/perlguts.pod
+++ b/pod/perlguts.pod
@@ -1957,15 +1957,34 @@ C<op_first> field but also an C<op_last> field.  The most complex type of
 op is a C<LISTOP>, which has any number of children.  In this case, the
 first child is pointed to by C<op_first> and the last child by
 C<op_last>.  The children in between can be found by iteratively
-following the C<op_sibling> pointer from the first child to the last.
+following the C<op_sibling> pointer from the first child to the last 9but
+see below).
 
-There are also two other op types: a C<PMOP> holds a regular expression,
+There are also some other op types: a C<PMOP> holds a regular expression,
 and has no children, and a C<LOOP> may or may not have children.  If the
 C<op_children> field is non-zero, it behaves like a C<LISTOP>.  To
 complicate matters, if a C<UNOP> is actually a C<null> op after
 optimization (see L</Compile pass 2: context propagation>) it will still
 have children in accordance with its former type.
 
+Finally, there is a C<LOGOP>, or logic op. Like a C<LISTOP>, this has one
+or more children, but it doesn't have an C<op_last> field: so you have to
+follow C<op_first> and then the C<op_sibling> chain itself to find the
+last child. Instead it has an C<op_other> field, which is comparable to
+the C<op_next> field described below, and represents an alternate
+execution path. Operators like C<and>, C<or> and C<?> are C<LOGOP>s. Note
+that in general, C<op_other> may not point to any of the direct children
+of the C<LOGOP>.
+
+Starting in version 5.21.2, perls built with the experimental
+define C<-DPERL_OP_PARENT> add an extra boolean flag for each op,
+C<op_lastsib>.  When set, this indicates that this is the last op in an
+C<op_sibling> chain. This frees up the C<op_sibling> field on the last
+sibling to point back to the parent op. The macro C<OP_SIBLING(o)> wraps
+this special behaviour, and always returns NULL on the last sibling.
+With this build the C<op_parent(o)> function can be used to find the
+parent of any op.
+
 Another way to examine the tree is to use a compiler back-end module, such
 as L<B::Concise>.