[OSM-dev] Disallowing certain characters in tag keys

[Tony Morris]

> The problem with disallowing special characters is that you "close the
> door". Software writers will then write software that depends on them
> not being there (or not caring which is probably the common case
> today). If we later find out that - for whatever reasons - we want to
> use one of those chars this will become extremely difficult, as it
> will cause trouble at many places in existing software.
>
This is an instance of what is called The Expression Problem.

-- 
Tony Morris
http://tmorris.net/