solve the XML declaration problem
diff --git a/R/column_spec.R b/R/column_spec.R
index f936305..7af7431 100644
--- a/R/column_spec.R
+++ b/R/column_spec.R
@@ -80,8 +80,7 @@
                                                "font-family: monospace;")
     }
   }
-  out <- structure(as.character(kable_xml), format = "html",
-                   class = "knitr_kable")
+  out <- as_kable_xml(kable_xml)
   attributes(out) <- kable_attrs
   return(out)
 }