@Override
    public boolean isValid(final int c) {
        return (c < 0x10000 && (CHARS[c] & MASK_VALID) != 0) ||
                (0x10000 <= c && c <= 0x10FFFF);
    }
Returns true if the specified character is valid. This method
also checks the surrogate character range from 0x10000 to 0x10FFFF.
<p>
If the program chooses to apply the mask directly to the
<code>CHARS</code> array, then they are responsible for checking
the surrogate character range.

@param c The character to check.
stroom-pipeline/src/main/java/stroom/pipeline/reader/Xml10Chars.java