fix Issue 2894 - abstract classes sometimes allow non-abstract bodyle…

…ss functions

function.dd

@@ -29,6 +29,20 @@ $(GNAME BodyStatement):
         This means they cannot be passed by reference to other functions.
         )
 
+<h3>Functions Without Bodies</h3>
+
+	$(P Functions without bodies:)
+
+---
+int foo();
+---
+
+	$(P that are not declared as $(D abstract) are expected to have their implementations
+	elsewhere, and that implementation will be provided at the link step.
+	This enables an implementation of a function to be completely hidden from the user
+	of it, and the implementation may be in another language such as C, assembler, etc.
+	)
+
 $(V2
 <h3>$(LNAME2 pure-functions, Pure Functions)</h3>