-A variable is a symbol associated with an integer value. The value of
-a variable is set by the @c SET action, and is referred by the @c SET,
-the @c INSERT, and the @c IF actions. All variables are implicitly
-initialized to zero.
+A variable is a symbol associated with an integer, a symbol, or an
+M-text value. The integer value of a variable can be set and referred
+by the @c SET action. It can be referred by the @c SET, the @c
+INSERT, the @c SELECT, the @c UNDO, the @c IF, the @c COND actions.
+The M-text value of a variable can be referred by the @c INSERT
+action. The symbol value of a variable can not be referred directly,
+is used the library implicitly (e.g. candidates-charset). All
+variables are implicitly initialized to the integer value zero.