Note that \var{ppos} values are not consecutive and should not be altered.
diff --git a/Doc/api/concrete.tex b/Doc/api/concrete.tex
index 67852db..c233ed4 100644
--- a/Doc/api/concrete.tex
+++ b/Doc/api/concrete.tex
@@ -1896,7 +1896,9 @@
parameters \var{pkey} and \var{pvalue} should either point to
\ctype{PyObject*} variables that will be filled in with each key and
value, respectively, or may be \NULL. Any references returned through
- them are borrowed.
+ them are borrowed. \var{ppos} should not be altered during iteration.
+ Its value represents offsets within the internal dictionary structure,
+ and since the structure is sparse, the offsets are not consecutive.
For example: