config-servlet/src/main/java/org/ocpsoft/rewrite/servlet/config/RequestParameter.java
public static RequestParameter valueExists(final String value)
   {
      return new RequestParameter("{" + RequestParameter.class.getName() + "_" + value + "_name}", value) {
         @Override
         public String toString()
         {
            return "RequestParameter.valueExists(\"" + value + "\")";
         }
      };
   }
public static RequestParameter valueExists(final String value)
   {
      return new RequestParameter("{" + RequestParameter.class.getName() + "_" + value + "_name}", value) {
         @Override
         public String toString()
         {
            return "RequestParameter.valueExists(\"" + value + "\")";
         }
      };
   }
Create a {@link Condition} that matches only against the existence of a request parameter value matching the given
pattern. The parameter name is ignored.
<p>
Parameter value expressions may be parameterized:
<p>
<code>
RequestParameter.valueExists("guest")<br/>
RequestParameter.valueExists("{username}")<br/>
...
</code>

@param name {@link ParameterizedPattern} matching the request parameter name.

@see ConfigurationRuleParameterBuilder#where(String) {@link HttpServletRequest#getParameterMap()}