How could you remove all characters that are not alphabetic from a string? What about non-alphanumeric? Does this have to be a custom function or are there also more generalizable solutions?

I need the list of ranges of Unicode characters with the property Alphabetic as defined in http://www.unicode.org/Public/5.1.0/ucd/UCD.html#Alphabetic. However, I cannot find them in the Unicode Ch...