这是什么原因？？

一个对密码进行修改的问题，以前别人做了一个，但他是这样写的，我不明白这段代码到底是什么意思？为什么要这样写？JSP里面是这样写的，代码如下： <table width="98%" border="0" align="center" cellpadding="0" cellspacing="0">
                        <tr>
                          <td width="60" align="right" nowrap>旧 口 令</td>
                          <td align="center" nowrap><html:password property = "value(pwd_old)" size="17" styleClass="T" /></td>
                        </tr>
                        <tr>
                          <td align="right" nowrap>&nbsp;</td>
                          <td align="center" nowrap>&nbsp;</td>
                        </tr>
                        <tr>
                          <td align="right" nowrap>新 口 令</td>
                          <td align="center" nowrap><html:password property = "value(pwd_new)" size="17" styleClass="T" /></td>
                        </tr>
                        <tr>
                          <td align="right" nowrap>&nbsp;</td>
                          <td align="center" nowrap>&nbsp;</td>
                        </tr>
                        <tr>
                          <td align="right" nowrap>确认口令</td>
                          <td align="center" nowrap><html:password property = "value(pwd_confirm)" size="17" styleClass="T" /></td>
                        </tr>
                        <tr>
                          <td align="right" colspan="2" nowrap><bing:error color="Red" size="4"/></td>
                        </tr>
                      </table>他这样写，我测试过，修改密码是没有问题的，我就不明白红字的部分的这段代码是什么意思，主要是这个：property = "value(pwd_old)" 为什么这样写，我也找了的，bean里面没有这个属性啊！
我就参照这个例子写，我的页面上就报这个错：
javax.servlet.ServletException: No getter method for property value(old_pw) of bean org.apache.struts.taglib.html.BEAN
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:825)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:758)
org.apache.jsp.system.userinfo.password_005fedit_jsp._jspService(password_005fedit_jsp.java:159)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
com.adr.common.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:40)不明白我参照这个例子做，为什么不行呢？诚恳的请教各位朋友！感谢！