grxml文件如下：

<?xml version="1.0"?>
<!DOCTYPE grammar PUBLIC "-//W3C//DTD GRAMMAR 1.0//EN"
         "http://www.w3.org/TR/speech-grammar/grammar.dtd">
<grammar mode="dtmf" version="1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.w3.org/2001/06/grammar
                             http://www.w3.org/TR/speech-grammar/grammar.xsd"
         xmlns="http://www.w3.org/2001/06/grammar">
<rule id="root">
<one-of>
   <item> 0 </item>
   <item> 1 </item>
   <item> 2 </item>
   <item> 3 </item>
   <item> 4 </item>
   <item> 5 </item>
   <item> 6 </item>
   <item> 7 </item>
   <item> 8 </item>
   <item> 9 </item>
</one-of>
</rule>

<rule id="pin" scope="public">
<one-of>
   <item>
     <item repeat="4"><ruleref uri="#digit"/></item>
     #
   </item>
   <item>
     * 9
   </item>
</one-of>
</rule>
</grammar>

vxml文件如下：
<?xml version="1.0" ?>
<!DOCTYPE vxml PUBLIC "-//W3C//DTD VOICEXML 2.1//EN" "http://www.w3.org/TR/voicexml21/vxml.dtd">
<vxml version="2.1" xmlns:xsi="http://www/w3/org/2001/vxml">

<form> <!-- If nothing else is specified, the first <form> that is encountered
   is used as initial dialog -->  
 <field name="ticket_num">
  <prompt>
     Read the 4 digit number from your ticket.
  </prompt>
   <help>The 4 digit number is to the lower left.</help>
   <grammar src="dtmf.grxml"
                 type="application/srgs+xml"/>
    <filled>
     <if cond="ticket_num.length != 4">
       <prompt>
          Sorry, I didn't hear exactly 4 digits.
       </prompt>
       <assign name="ticket_num" expr="undefined"/>
     <else/>
       <prompt>
          I heard <say-as interpret-as="vxml:digits">
          value expr="ticket_num"/></say-as>
       </prompt>
     </if>
  </filled>
 </field>
      </form>
</vxml>

我用的是openvxi来跑vxml的，如果输入一个字符串，就会返回no match，只能
一个个字符输入，但是输入一个字符的又不会去match，这个怎么处理呢？