Added additional information about compound keys and null/default values.

README.md

@@ -270,9 +270,29 @@ example:
 
 By taking advantage of reflection and bean-property-style lookups, you can do kooky things:
 
-    Mustache.compiler().compile("Hello {{this.class.name}}!").execute(new Object());
+    Mustache.compiler().compile("Hello {{class.name}}!").execute(new Object());
     // result: Hello java.lang.Object!
 
+Note that compound variables are essentially short-hand for using singleton
+sections. The above examples could also be represented as:
+
+    "Hello {{#field}}{{who}}{{/field}}"
+    "Hello {{#class}}{{name}}{{/class}}"
+
+Note also that one semantic difference exists between nested singleton sections
+and compound variables: compound variables do not make use of the default value
+and null value configuration. If a null or missing value is encountered while
+resolving a compound section, an exception is always raised.
+
+If you desire for a default value to be used when null or missing values are
+encountered, use the somewhat more verbose singleton sections. The use of
+sections clearly communicates to someone reading the template that the section
+will not be rendered if the object it references is missing or null and allows
+for a site-specific default value to be used, as in:
+
+    {{#foo}}{{name}}{{/foo}}
+    {{^foo}}Missing foo!{{/foo}}
+
 Newline trimming
 ----------------