Update header.html
diff --git a/doc/doxyfile.in b/doc/doxyfile.in
index 57c61c2..7265a22 100644
--- a/doc/doxyfile.in
+++ b/doc/doxyfile.in
@@ -984,7 +984,8 @@
 # classes, structs, unions or interfaces.
 # The default value is: YES.
 
-ALPHABETICAL_INDEX     = NO
+ALPHABETICAL_INDEX     = YES
+TOC_INCLUDE_HEADINGS = 2
 
 # The COLS_IN_ALPHA_INDEX tag can be used to specify the number of columns in
 # which the alphabetical index list will be split.