runtime(doc): Clarify list-concatenation a bit more

Make doc list-concatenation more clear as for += and extend().

1. describe `+=` for list-concatenation more accurately
2. add `extend()` example for list-concatenation
3. Fix CI errors for missing helptags reference |+=|

closes: #13983

Signed-off-by: qeatzy <qeatzy@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 75ea2c7f4260b4b73d1a5deb328a14a033c648ab..3dbbbeafb2b43fed90d82dee052cd979aa4ea19f 100644 (file)
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1,4 +1,4 @@
-*eval.txt*     For Vim version 9.1.  Last change: 2024 Feb 06
+*eval.txt*     For Vim version 9.1.  Last change: 2024 Feb 07
 
 
                  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -303,7 +303,9 @@ List concatenation ~
                                                        *list-concatenation*
 Two lists can be concatenated with the "+" operator: >
        :let longlist = mylist + [5, 6]
+A list can be concatenated with another one in place using the "+=" operator or |extend()|: >
        :let mylist += [7, 8]
+       :call extend(mylist, [7, 8])
 
 To prepend or append an item, turn the item into a list by putting [] around
 it.  To change a list in-place, refer to |list-modification| below.
@@ -425,7 +427,8 @@ To change part of a list you can specify the first and last item to be
 modified.  The value must at least have the number of items in the range: >
        :let list[3:5] = [3, 4, 5]
 
-To add items to a List in-place, you can use the |+=| operator: >
+To add items to a List in-place, you can use the += operator
+|list-concatenation|: >
        :let listA = [1, 2]
        :let listA += [3, 4]
 <