That's actually problematic all by itself. Parsers have no way of
telling from the data they've been presented which characters are valid.
That's technically true, but the same is true, e.g., of Java and many other languages, and for the same reasons. Fortunately, the list of valid characters only expands, it never shrinks.
--
Her he asked if O'Hare Doctor tidings sent from far coast and she with
grameful sigh him answered that O'Hare Doctor in heaven was. Sad was the
man that word to hear that him so heavied in bowels ruthful. All she
there told him, ruing death for friend so young, algate sore unwilling
God's rightwiseness to withsay. Joyce, Ulysses, "Oxen of the Sun"
