+
+<enumref ref="identifier">enum item identifier</enumref>
+
+ This element represents a reference to item of enum.
+
+<unop op="operator">expression</unop>
+
+ This element represents a unary operator, with the op attribute specifying
+ which operator. The only supported operation so far is ~, and its semantic
+ is identical to the corresponding operator in C.
+
+<sumof ref="identifier" />
+
+ This element represents a sumation of the elements of the referenced list.
+
+<popcount>expression</popcount>
+
+ This element represents the number of bits set in the expression.
+