@Override
    public boolean isValidLiteral(int c) {
        return ((c < 0x10000 && ((XML11CHARS[c] & MASK_XML11_VALID) != 0
                && (XML11CHARS[c] & MASK_XML11_CONTROL) == 0))
                || (0x10000 <= c && c <= 0x10FFFF));
    }
Returns true if the specified character is valid and not a control
character.
This method also checks the surrogate character range from 0x10000 to 0x10FFFF.

@param c The character to check.
stroom-pipeline/src/main/java/stroom/pipeline/reader/Xml11Chars.java