patch 8.2.4726: cannot use expand() to get the script name

Problem:    Cannot use expand() to get the script name.
Solution:   Support expand('<script>'). (closes #10121)
diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index 0867c47..cd9b988 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -939,7 +939,7 @@
 		   file name of the sourced file.  *E498*
 		   When executing a legacy function, is replaced with the call
 		   stack, as with <stack> (this is for backwards
-		   compatibility, using <stack> is preferred).
+		   compatibility, using <stack> or <script> is preferred).
 		   In Vim9 script using <sfile> in a function gives error
 		   *E1245* .
 		   Note that filename-modifiers are useless when <sfile> is
@@ -951,6 +951,12 @@
 		   ".." in between items.  E.g.:
 		   "function {function-name1}[{lnum}]..{function-name2}[{lnum}]"
 		   If there is no call stack you get error *E489* .
+							*:<script>* *<script>*
+	<script>   When executing a `:source` command, is replaced with the file
+		   name of the sourced file.  When executing a function, is
+		   replaced with the file name of the script where it is
+		   defined.
+		   If the file name cannot be determined you get error *E1274* .
 							*:<slnum>* *<slnum>*
 	<slnum>	   When executing a ":source" command, is replaced with the
 		   line number.  *E842*