In Commerce Reference Store, there is an instance of the SearchBox cartridge called Search Box, located in /content/Shared/Global Search Configuration/Search Box in Experience Manager. The <crs:pageContainer.tag> retrieves the contents of the Search Box cartridge to render the search box that appears in the header portion of each page. To do this, the <crs:pageContainer.tag> calls the /atg/endeca/assembler/droplet/InvokeAssembler servlet bean and passes in the full path to the cartridge:

<dsp:droplet name="InvokeAssembler">
  <dsp:param name="contentCollection"
             value="/content/Shared/Global Search Configuration/Search Box"/>
  <dsp:oparam name="output">
    <dsp:getvalueof var="searchBox"
                    vartype="com.endeca.infront.assembler.ContentItem"
                    param="contentItem" />
  </dsp:oparam>
</dsp:droplet>