Allow rules to declare they only accept a set of options (#1560)

src/main/java/carpet/api/settings/CarpetRule.java

@@ -85,6 +85,18 @@ public interface CarpetRule<T> {
      */
     T defaultValue();
     
+    /**
+     * <p>Returns whether this rule is strict.</p>
+     * 
+     * <p>A rule being strict means that it will only accept the suggestions returned by {@link #suggestions()} as valid values.</p>
+     * 
+     * <p>Note that a rule implementation may return {@code false} in this method but still not accept options other than those
+     * returned in {@link #suggestions()}, only the opposite is guaranteed.</p>
+     */
+    default boolean strict() {
+        return false;
+    }
+    
     /**
      * <p>Sets this rule's value to the provided {@link String}, after first converting the {@link String} into a suitable type.</p>
      *