How to check that all string characters are ASCII? It is sad in [documentation](http://wiki.freepascal.org/LCL_Unicode_Support):

> 
> Unicode characters U+0000 to U+007F (ASCII) are encoded simply as
>  bytes 00h to 7Fh (ASCII compatibility). This means that files and
>  strings which contain only 7-bit ASCII characters have the same
>  encoding under both ASCII and UTF-8. All characters >U+007F are
>  encoded as a sequence of several bytes, each of which has the two most
>  significant bits set.
> 
> 
> 

So I wonder how to check string to be ASCII?