diff --git a/docs/doc-geo.txt b/docs/doc-geo.txt
index 26b5085..e3ed31e 100644
--- a/docs/doc-geo.txt
+++ b/docs/doc-geo.txt
@@ -3,6 +3,10 @@ devil1geo.h / devil1geo.c
     Handles files containing geometry.
 
 Functions
+    All functions are static but exposed by a function pointer in a constant
+    struct called DEVIL1GEO. For example, clients call functions using
+    DEVIL1GEO.printheader(...);
+
     void printheader(struct Header*);
         Show attributes and values of a Header for the package.