diff --git a/lisp/nxml/rng-match.el b/lisp/nxml/rng-match.el
index e767a9333b5..f3549681f25 100644
--- a/lisp/nxml/rng-match.el
+++ b/lisp/nxml/rng-match.el
@@ -1154,7 +1154,7 @@ list may contain duplicates."
 	     (if (or (rng--ipattern-nullable
 		      (rng-data-deriv child value))
 		     (and (rng--ipattern-nullable child)
-			  (rng-blank-p value)))
+                          (string-blank-p value)))
 		 (rng--ipattern-after ipattern)
 	       rng-not-allowed-ipattern)))
 	  ((eq type 'data)
diff --git a/lisp/nxml/rng-parse.el b/lisp/nxml/rng-parse.el
index 76cb94b144c..1c08d77f56f 100644
--- a/lisp/nxml/rng-parse.el
+++ b/lisp/nxml/rng-parse.el
@@ -62,7 +62,7 @@ be signaled in the same way as when it is not well-formed."
 	 (unless (rng-match-element-value (or text ""))
 	   (cons "Invalid data" (and text 'text))))
 	((and text
-	      (not (rng-blank-p text))
+              (not (string-blank-p text))
 	      (not (rng-match-mixed-text)))
 	 (cons "Text not allowed" 'text))
 	((not start-tag)
diff --git a/lisp/nxml/rng-util.el b/lisp/nxml/rng-util.el
index 74f405410ac..da51e81dbe7 100644
--- a/lisp/nxml/rng-util.el
+++ b/lisp/nxml/rng-util.el
@@ -36,8 +36,6 @@
 
 (defconst rng-builtin-datatypes-uri (rng-make-datatypes-uri ""))
 
-(defun rng-blank-p (str) (string-match "\\`[ \t\n\r]*\\'" str))
-
 (defun rng-substq (new old list)
   "Replace first member of LIST (if any) that is `eq' to OLD by NEW.
 LIST is not modified."
@@ -84,13 +82,12 @@ LIST is not modified."
 
 (define-error 'rng-error nil)
 
-;; Obsolete.
-
 (defun rng-uniquify-eq (list)
   (declare (obsolete seq-uniq "28.1"))
   (seq-uniq list #'eq))
 
 (define-obsolete-function-alias 'rng-uniquify-equal #'seq-uniq "28.1")
+(define-obsolete-function-alias 'rng-blank-p #'string-blank-p "29.1")
 
 (provide 'rng-util)
 
diff --git a/lisp/nxml/rng-valid.el b/lisp/nxml/rng-valid.el
index b9c980222e2..ad5c9c7a15c 100644
--- a/lisp/nxml/rng-valid.el
+++ b/lisp/nxml/rng-valid.el
@@ -1275,7 +1275,7 @@ Return nil at end of buffer, t otherwise."
 
 (defun rng-segment-blank-p (segment)
   (if (car segment)
-      (rng-blank-p (car segment))
+      (string-blank-p (car segment))
     (apply #'rng-region-blank-p
 	   (cdr segment))))
 
@@ -1303,7 +1303,7 @@ string between START and END."
 	((not (or (and whitespace
 		       (or (eq whitespace t)
 			   (if value
-			       (rng-blank-p value)
+                               (string-blank-p value)
 			     (rng-region-blank-p start end))))
 		  (rng-match-mixed-text)))
 	 (rng-mark-invalid "Text not allowed" start (or end (point))))))