use new memo feature of zsh to find item in region_highlight

exchange

@@ -2,15 +2,23 @@
 
 setopt localoptions noksharrays
 
-local colour
+local colour memo="memo=zsh-viexchange"
 local pos1 pos2 swap nl1 nl2
 local _save_cur _save_cut="$CUTBUFFER"
 local REPLY
 
 zstyle -s zle:$WIDGET highlight colour || colour='fg=26,bg=195'
 
 # retrieve first exchange selection
-pos2=( ${(M)region_highlight:#* $colour} )
+pos2=( ${(M)region_highlight:#*$memo*} ) # try memo feature
+if (( ! $#pos2 )); then
+  region_highlight+=( " 0 0 fg=red, $memo" )
+  if [[ ${region_highlight[-1]} = "0 0 fg=red" ]]; then
+    # zsh 5.8 or earlier, search for entry by colour
+    pos2=( ${(M)region_highlight:#* $colour} )
+  fi
+  region_highlight[-1]=()
+fi
 
 # check if we should clear the selection or select a line
 if [[ $WIDGET = *-line ]]; then
@@ -61,6 +69,6 @@ if (( $#pos2 )); then
     BUFFER[1+pos1[1],pos1[2]]="$swap$nl1"
   fi
 elif (( $#pos1 )); then
-  region_highlight+=( "$pos1[1] $pos1[2] $colour")
+  region_highlight+=( "$pos1[1] $pos1[2] $colour, $memo")
 fi
 CUTBUFFER="$_save_cut" CURSOR="$_save_cur"