Lua scripting/Requirements

Here is a list of thing which are possibly necessary for end-users (found by polling random template writers):
 * String functions and regular expressions — requested by most users whom I asked. Essentially one of the reasons why
 * Functions.
 * Proper error reporting. If an error occurred on certain wiki page, there should be a traceback which lists all modules and the line on which the error occurred.
 * Image output.

TODO: ask more users. Open a village pump discussion about that.

Here is a list of things we would probably want to do as well:
 * Global scripts
 * Code editor
 * Debugging tools

Here are potential implementation obstacles:
 * Lua has a feature called "pattern matching". This is essentially a regular expressions, but with their own special features. They are not Perl-compatible unlike what most of Wikipedia use.
 * Image output sounds like something that has a rather low priority.
 * Lua seems to have issues with error handling. Apparently it does not have proper exceptions.
 * The main issue with global scripts is to invalidate the cache on local wikis when a global script is changed.