Add new function 'add-display-text-property'

* doc/lispref/display.texi (Display Property): Document it.
* lisp/emacs-lisp/subr-x.el (add-display-text-property): New function.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/subr-x-tests.el b/test/lisp/emacs-lisp/subr-x-tests.el
index f9cfea888c7..69d59e84f6d 100644
--- a/test/lisp/emacs-lisp/subr-x-tests.el
+++ b/test/lisp/emacs-lisp/subr-x-tests.el
@@ -676,5 +676,23 @@
       (buffer-string))
     "foo\n")))
 
+(ert-deftest test-add-display-text-property ()
+  (with-temp-buffer
+    (insert "Foo bar zot gazonk")
+    (add-display-text-property 4 8 'height 2.0)
+    (add-display-text-property 2 12 'raise 0.5)
+    (should (equal (get-text-property 2 'display) '(raise 0.5)))
+    (should (equal (get-text-property 5 'display)
+                   '((raise 0.5) (height 2.0))))
+    (should (equal (get-text-property 9 'display) '(raise 0.5))))
+  (with-temp-buffer
+    (insert "Foo bar zot gazonk")
+    (put-text-property 4 8 'display [(height 2.0)])
+    (add-display-text-property 2 12 'raise 0.5)
+    (should (equal (get-text-property 2 'display) '(raise 0.5)))
+    (should (equal (get-text-property 5 'display)
+                   [(raise 0.5) (height 2.0)]))
+    (should (equal (get-text-property 9 'display) '(raise 0.5)))))
+
 (provide 'subr-x-tests)
 ;;; subr-x-tests.el ends here