patch 9.1.1426: completion: register contents not completed

Problem:  CTRL-X CTRL-R only completes individual words from registers,
          making it difficult to insert complete register content.
Solution: Add consecutive CTRL-X CTRL-R support - first press completes
          words, second press completes full register lines, similar to
          CTRL-X CTRL-L and CTRL-X CTRL-P behavior (glepnir).

closes: #17395

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 553183d..9ec4682 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -1,4 +1,4 @@
-*insert.txt*    For Vim version 9.1.  Last change: 2025 May 26
+*insert.txt*    For Vim version 9.1.  Last change: 2025 Jun 02
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -649,7 +649,7 @@
 11. omni completion					|i_CTRL-X_CTRL-O|
 12. Spelling suggestions				|i_CTRL-X_s|
 13. keywords in 'complete'				|i_CTRL-N| |i_CTRL-P|
-14. words from registers				|i_CTRL-X_CTRL-R|
+14. contents from registers				|i_CTRL-X_CTRL-R|
 
 Additionally, |i_CTRL-X_CTRL-Z| stops completion without changing the text.
 
@@ -1021,7 +1021,7 @@
 				:imap <Tab> <C-X><C-V>
 
 
-Completing words from registers				*compl-register-words*
+Completing contents from registers			*compl-register-words*
 							*i_CTRL-X_CTRL-R*
 CTRL-X CTRL-R		Guess what kind of item is in front of the cursor from
 			all registers and find the first match for it.
@@ -1035,6 +1035,11 @@
 	CTRL-P		Search backwards for previous match.  This match
 			replaces the previous one.
 
+	CTRL-X CTRL-R	Further use of CTRL-X CTRL-R will copy the line
+			following the previous expansion in other contexts
+			unless a double CTRL-X is used (e.g. this switches
+			from completing register words to register contents).
+
 User defined completion					*compl-function*
 
 Completion is done by a function that can be defined by the user with the