[[http://www.lua.org/manual/5.1/manual.html#5.4.1]]
[[https://www.gammon.com.au/scripts/doc.php?lua=string.find]]

=== escape special characters for pattern matching ===
<code lua>
pattern = pattern:gsub ("%+", "%%%+") -- change '+' to '%+'
pattern = pattern:gsub("([+%?])", "%%%1") -- escape only characters from set
pattern = pattern:gsub("([^%w])", "%%%1") -- escape all non alphanumeric characters
</code>