On behalf of its CBSX stock exchange, CBOE filed for immediate effectiveness to adopt 3 forms of Self-Trade Prevention modifiers - Cancel Newest, Cancel Oldest, Cancel Both.  A CBSX Trader may elect for all of his proprietary orders and quotes to be marked with a Self-Trade Prevention modifier, and in doing so, will prevent any quote or order he submits from being executed against a resting opposite side order or quote that is labeled as originating from the same associated acronym and trading for the same account (for the purposes of this Rule, the "Same CBSX Trader"). CBSX System Configuration. Due to system limitations, Self-Trade Prevention elections cannot be made on a per-order, per-quote, or security-by-security basis.  Accordingly, a CBSX Trader may only elect one of the 3 Self-Trade Prevention options, and that election shall apply to all of the CBSX Trader's eligible prop orders and quotes. These modifiers have limited use - i.e., they shall apply only to prop orders and quotes.  The purpose of limiting the Self-Trade  Prevention modifiers to prop orders and quotes is to avoid preventing agency orders from trading with each other, as agency orders for the same CBSX Trader may actually be for different customers. How the 'Cancel Newest' Modifier Works. If a CBSX Trader has made the election for the Cancel Newest Self-Trade Prevention modifier, any incoming order or quote submitted by that CBSX Trader will not execute against opposite side resting interest from the Same CBSX Trader. The incoming order or quote (or any portion thereof) will be canceled back to the originating CBSX Trader if such order or quote cannot trade with another eligible order or quote originating from any origin other than the Same CBSX Trader. The resting order or quote from the Same CBSX Trader will remain on the book. In the case of an opening or re-opening, the newer of the two orders or quotes submitted by the Same CBSX Trader will be canceled, and the older order or quote will permitted to trade with eligible orders or quotes originating from any origin other than the Same CBSX Trader, and any remaining portion thereof will be entered into the book.

Cancel Newest Example 1: An order to buy 500 shares @ $20.00 from a CBSX Trader who has elected for the Cancel Newest Self-Trade Prevention modifier rests on the CBSX Book with no resting interest behind it. An order to sell 500 shares @ $20.00 comes in from the Same CBSX Trader. The incoming sell order for 500 shares @ $20.00 is then canceled back to the originating CBSX Trader. The resting buy order for 500 shares @ $20.00 remains on the CBSX Book.

Cancel Newest Example 2: An order to buy 500 shares @ $20.00 from a CBSX Trader who has elected for the Cancel Newest Self-Trade Prevention modifier rests on the CBSX Book with another order to buy 500 shares @ $20.00 from another CBSX Trader resting behind it. An order to sell 500 shares @ $20.00 comes in from the Same CBSX Trader. The incoming sell order for 500 shares @ $20.00 would not trade with the order to buy 500 shares @ $20.00 from the Same CBSX Trader, but would trade with the order to buy 500 shares @ $20.00 from the other CBSX Trader resting behind the buy order from the Same CBSX Trader. That resting buy order for 500 shares @ $20.00 from the Same CBSX Trader remains on the CBSX Book.

Cancel Newest Example 3: An order to buy 500 shares @ $20.00 from a CBSX Trader who has elected for the Cancel Newest Self-Trade  Prevention modifier rests on the CBSX Book with no resting interest behind it. An order to sell 700 shares @ $20.00 comes in from the Same CBSX Trader. The incoming sell order for 700 shares @ $20.00 is then canceled back to the originating CBSX Trader. The resting buy order for 500 shares @ $20.00 remains on the CBSX Book.

The rule filing documents additional pages of examples for all three modifiers, along with other detailed guidelines. To continue reading, go to:   [CBOE Rule Filing 12-13, 2/16/12].