+ *
+ * An extra note for message/external-body parts. The enclosing
+ * content structure is marked as a message/external-body; the c_ctparams
+ * contains a pointer to a struct exbody, which contains a pointer to
+ * (among other things) the "real" content (e.g., application/octet-stream).
+ * The "real" content structure has the c_ctexbody pointer back to the
+ * same struct exbody sees in the enclosing content structure (the struct
+ * exbody contains parent pointers if you need to traverse up the content
+ * structure). Hopefully this makes it clearer:
+ *
+ * Enclosing content:
+ * Type: message/external-body
+ * c_ctparams: pointer to "struct exbody"
+ * c_ctexbody: NULL
+ *
+ * "Real" content:
+ * Type: application/octet-stream (or whatever)
+ * c_ctparams: NULL
+ * c_ctexbody: pointer to "struct exbody"
+ *