need suggestion for looping and variable problem

Hi, 
I have an email app that allow user to select email_msg serverl times 
and concat the messages. 

But, I can't do this cuz it is return just only one value 
MAILMSGCONTENT. 

<select name="MAILMSGCONTENT" title="MAILMSGCONTENT" multiple="false">
<xsl:for-each select="( user_email_msgs/email_msg | 
default_email_msgs/email_msg ) [position() > ($Page * $PageSize)] 
[position() &lt;= $PageSize]">
            <option value="{em_msg_subj}" onpick="#editMsg" >
                <xsl:value-of select="em_msg_subj"/>
            </option>
        </xsl:for-each>
</select>

What I want is: 
The first time, when user click one msg(yes), it return (yes)
The second time, when user click another one(no), it return (no) and  
I'll concat it to become (yes; no)
How can I approach this? any ideas? Thanks in advance. 

--xml
<?xml version="1.0"?>
    <user_email_msgs usr_id="user1">
      <email_msg>
        <em_msg_subj>Are you testing?</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>How are you doing?</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>Please call</em_msg_subj>
      </email_msg>
    </user_email_msgs>
    <default_email_msgs>
      <email_msg>
        <em_msg_subj>Yes</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>No</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>Please call</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>Pick Up Groceries</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>Call Home</em_msg_subj>
      </email_msg>
      <email_msg>
        <em_msg_subj>Contact School</em_msg_subj>
      </email_msg>
    </default_email_msgs>


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