When will tag liferay-portlet:renderURLParams be needed?

[Kurt Xu, módosítva 11 év-val korábban]

Hi all:
I'm new to liferay development. I discover that submitting form won't make page move without a liferay-portlet:renderURLParams inside the form when I want to search something by the keywords input. What use is liferay-portlet:renderURLParams?
Related code snippet is as below:

<portlet:renderurl var="addSloganURL">
    <portlet:param name="jspPage" value="/html/edit_slogan.jsp" />
</portlet:renderurl>

<c:if test="<%= PortletPermissionUtil.contains(permissionChecker, portletDisplay.getId(), &quot;ADD_SLOGAN&quot;) %>">
    <input type="button" value="<liferay-ui:message key=" add-slogan">" onClick="location.href =
    '&lt;%= addSloganURL.toString() %&gt;';" /&gt;
</c:if>

&lt;%
    String tabs1 = ParamUtil.getString(request, "tabs1", "by-rating");

    String tabs1Values = "by-rating,by-date";

    PortletURL tabsURL = renderResponse.createRenderURL();
    tabsURL.setParameter("jspPage", "/html/view.jsp");
    tabsURL.setParameter("tabs1", tabs1);

    PortletURL iteratorURL = renderResponse.createRenderURL();
    iteratorURL.setParameter("tabs1", tabs1);

%&gt;

<liferay-portlet:renderurl varimpl="searchURL">
    <portlet:param name="jspPage" value="/html/search.jsp" />
</liferay-portlet:renderurl>

<aui:form action="<%= searchURL %>" method="get" name="fm0">
    <liferay-portlet:renderurlparams varImpl="searchURL" />
    <aui:input name="redirect" type="hidden" value="<%= currentURL %>" />
    <aui:input name="groupId" type="hidden" value="<%= String.valueOf(scopeGroupId) %>" />

    <div class="portlet-toolbar search-form">
    <span class="aui-search-bar">
       <aui:input inlineField="<%= true %>" label="" name="keywords" size="30" title="search-entries" type="text" />

       <aui:button type="submit" value="search" />
    </span>
    </div>
</aui:form>

It's from sample code Slogan contest portlet from Liferay In Action.
Thanks.