OUTER
    ...stuff...
    INNER
        ...stuff...     
    END
    INNER
        ...stuff...
    END
    ...stuff...
END

private class OuterBlockRule extends MultiLineRule {

	public OuterBlockRule(IToken token) {
		super("OUTER", "END", token);
	}

	@Override
	protected boolean endSequenceDetected(ICharacterScanner scanner) {
		int readCount = 0;
		int c;
		while ((c = scanner.read()) != ICharacterScanner.EOF) {
			if ((fEndSequence.length > 0 && c == fEndSequence[0])
					&& sequenceDetected(scanner, fEndSequence, fBreaksOnEOF)
					&& correctEndSequenceDetected(scanner)) {
				return true;
			}
			++readCount;
		}
		for ( ; readCount > 0; readCount--) {
			scanner.unread(); // Rewind scanner back to where we started
		}
		return false;
	}

	/**
	 * Returns <code>true</code> if this end sequence belongs to
	 * <code>OUTER</code>, not <code>INNER</code>
	 */
	private boolean correctEndSequenceDetected(ICharacterScanner scanner) {
		StringBuffer buffer = new StringBuffer();

		// Scan all the way back to OUTER
		scanner.read();
		do {
			scanner.unread(); // Rewind before last read char
			scanner.unread(); // Rewind before first unread char
			buffer.insert(0, (char) scanner.read());

		} while (!startsWithOuter(buffer));

		// Reset scanner back to the position where we started
		for (int i = 0, n = buffer.length(); i < n; i++) {
			scanner.read();
		}

		// Count occurrences of INNER and END
		int innerCount = 0;
		int endCount = 0;
		for (String line : buffer.toString().split("\n")) {
			String l = line.trim();
			if (l.startsWith("INNER")) {
				++innerCount;
			} else if (l.startsWith("END")) {
				++endCount;
			}
		}

		// If there is 1 more occurrence of END than INNER, this END must
		// belong to OUTER
		return (endCount == (innerCount + 1));
	}

	private boolean startsWithOuter(StringBuffer buffer) {
		// Ignore words which appear in an unterminated string
		return buffer.toString().startsWith("OUTER")
				&& allStringsTerminated(buffer);
	}

	/**
	 * Returns <code>true</code> if all strings are terminated, i.e. an even
	 * number of ' chars are found
	 */
	private boolean allStringsTerminated(StringBuffer buffer) {
		int count = 0;
		for (Character c : buffer.toString().toCharArray()) {
			if (c == '\'') {
				++count;
			}
		}
		return ((count % 2) == 0);
	}

}