vim-patch:ffc89e4 runtime(doc): clarify complete_match() and 'isexpand' option

clarify complete_match() documentation to better explain its backward
search behavior, argument handling, and return value format and add an
example of isexpand

closes: https://github.com/vim/vim/pull/17212

ffc89e47d0

runtime/lua/vim/_meta/options.lua

@@ -3439,6 +3439,13 @@ vim.bo.inf = vim.bo.infercase
 --- Note: Use "\\," to add a literal comma as trigger character, see
 --- `option-backslash`.
 ---
+--- Examples:
+---
+--- ```vim
+---     set isexpand=.,->,/*,\\,
+--- ```
+---
+---
 --- @type string
 vim.o.isexpand = ""
 vim.o.ise = vim.o.isexpand