private void growIndentChars(final int len) {
        if (len >= indentChars.length) {
            int increment = 5 * indentation;
            if (len > indentChars.length + increment) {
                increment += len;
            }
            final char[] tmp = new char[indentChars.length + increment];
            System.arraycopy(indentChars, 0, tmp, 0, indentChars.length);
            Arrays.fill(tmp, indentChars.length, tmp.length, ' ');
            indentChars = tmp;
        }
    }
Test whether the given character is a high surrogate

@param ch The character to test.
@return true if the character is the first character in a surrogate pair
stroom-pipeline/src/main/java/stroom/pipeline/xml/util/XMLWriter.java