Re: How to filter characters from a string?

Perhaps I misunderstand what you're trying to do.

You seem to be confusing the act of discarding information with
the act of encoding it.

Base64 is a means of encoding binary data as a sequence of ASCII
characters which are known to survive simpleminded text transmission
protocols like SMTP.  The Base64 encoding and decooding operations
are inverses of each other.  The original sequence of 8 bit bytes
is recovered as a result of decoding.

Taking a body of text and removing any character is that is not 
one of the output characters of the Base64 encoding operation is
not the same as encoding that text.

What are you really trying to do?

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