<span mo:type="FileBox" mo:name="${fieldName}" 
        mo:props="
          uploadId        : 'x123', 
          allowedExts     : '.gif;.jpg', 
          busyImage       : '*', 
          onFileSelectHandler : OnFileSelect, 
          onFileUploadHandler : OnFileUpload, 
          nonBlank        : ${nonBlank}, 
          valHandler      : ${valHandler}, 
          valErrorHandler : ${valErrorHandler}
       ">
    <input name="elm" type="text" readonly="readonly" value="${value}" />
    <input name="opener" type="button" value="Upload..."  />
  </span>

${fieldName}

The name of the ProcessField

${initialValue}

The initial value of the field

${nonBlank}

If "true" then the field cannot be left blank

${valHandler}

The name of the validation handler function

${valErrorHandler}

The name of the validation error handler function