code: protected String defaultActionHtml() {
  
          StringBuffer result = new StringBuffer(32);
  
          result.append(htmlStart());
          result.append(bodyStart(null));
          result.append(dialogStart());
          result.append(dialogContentStart(""));
          result.append("<form name=\"main\" class=\"nomargin\" action=\"");
          result.append(getJsp().link(getDialogReturnUri()));
          result.append("\" method=\"post\" onsubmit=\"submitAction('");
          result.append(DIALOG_OK);
          result.append("', null, 'main');\" enctype=\"multipart/form-data\">\n");
          result.append(paramsAsHidden());
          if (getParamFramename() == null) {
              result.append("<input type=\"hidden\" name=\"");
              result.append(PARAM_FRAMENAME);
              result.append("\" value=\"\">");
          }
          result.append(createDialogErrorMessage());
          result.append(dialogBlockStart(getStarttext()));
          result.append("<table border=\"0\" width=\"100%\">\n");
          result.append("<tr>\n\t<td style=\"white-space: nowrap;\" unselectable=\"on\">");
          result.append(getImportMessage());
          result.append(":</td>\n");
          result.append("\t<td class=\"maxwidth\">");
          result.append("<input type=\"file\" name=\"");
          result.append(PARAM_IMPORTFILE);
          result.append("\" class=\"maxwidth\" accept=\"application/zip\">");
          result.append("</td>\n</tr>");
          result.append(getAdditionalParameters());
          result.append("</table>\n");
          result.append(dialogBlockEnd());
  
          result.append(dialogContentEnd());
          result.append(dialogButtonsOkCancel());
          result.append("</form>\n");
          result.append(dialogEnd());
          result.append(bodyEnd());
          result.append(htmlEnd());
          return result.toString();
      }
docs: Returns the HTML to build the input form of the upload dialog.<p>
  
  @return the HTML to build the input form of the upload dialog