3.2.15. CHARS([streamid])

Returns the number of characters left in the named streamid, or
the default input stream if streamid is unspecified. For transient
streams this will always be either 1 if more characters are
available, or 0 if the End-Of-File condition has been met. For
persistent streams the number of remaining bytes in the file will
be possible to calculate and the true number of remaining bytes
will be returned.

However, on some systems, it is difficult to calculate the number
of characters left in a persistent stream; the requirements to
CHARS() has therefore been relaxed, so it can return 1 instead of
any number other than 0. If it returns 1, you can therefore not
assume anything more than that there is at least one more
character left in the input stream.

     CHARS()        –>   ‘1’  /* more data on def. input stream */
     CHARS()        –>   ‘0’  /* EOF for def. input stream */
     CHARS(‘outdata’)    –>   ‘94’  /* maybe */


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