It will make sure the language names start with an alphabetic character, followed by any number of [A-za-z0-9#_+] using the sed program. The # is for C# and + for C++ and _ for good measure.

> 
>> You don't know in advance what flag that would be and what it would mean
>> in compadd (you need to consider future compadd too), so this is
>> essentially undefined behaviour.