Index: trunk/doc/modules/CameraImages.tex
===================================================================
--- trunk/doc/modules/CameraImages.tex	(revision 5377)
+++ trunk/doc/modules/CameraImages.tex	(revision 5485)
@@ -307,4 +307,17 @@
 \code{false}.  If all the \code{parent} pointers were correct, the
 function shall return \code{true}.
+
+
+Each of the levels in the hierarchy have a place to hold a
+\code{p_pmHDU}, which is the disk representation of the image:
+\begin{datatype}
+typedef struct {
+    const char *extname;		// Extension name, if it corresponds to this level
+    psMetadata *header;			// The FITS header, if it corresponds to this level
+    psArray *images;			// The pixel data, if it corresponds to this level
+    psArray *masks;			// The mask data, if it corresponds to this level
+    psArray *weights;			// The weight data, if it corresponds to this level
+} p_pmHDU;
+\end{datatype}
 
 \subsection{Detector Coordinate Transformations}