The CBOE Stock Exchange (CBSX) proposes to adopt 3 forms of Self-Trade Prevention modifiers: (i) Cancel Newest, (ii) Cancel Oldest, (iii) Cancel Both ... Self-Trade Prevention modifiers.  As proposed, a CBSX Trader may elect for all of his proprietary orders and quotes to be marked with a Self-Trade Prevention modifier. If a CBSX Trader makes such an election, then any quote or order that's submitted will be prevented from executing 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"). One Election Only. A CBSX Trader may only elect for one of the 3 Self-Trade Prevention options, as the CBSX System may only be configured to permit one such election.  Such election shall apply to all of the CBSX Trader’s eligible proprietary orders and quotes.  As such, Self-Trade Prevention elections cannot be made on a per-order, per-quote, or security-by-security basis due to CBSX System limitations.  Any of the Cancel Newest, Cancel Oldest, or Cancel Both Self-Trade Prevention modifiers may be accommodated on the CBSX System. Limited Application of Modifier. The Self-Trade Prevention modifiers only apply to proprietary orders and quotes.  The purpose of limiting the Self-Trade Prevention modifiers to proprietary 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. In circumstances in which both the Market-Maker Trade Prevention Order and a Self-Trade Prevention Modifier are implicated, the Self-Trade Prevention Modifier shall rule and take precedence. Cancel Newest. 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 ("Another CBSX Trader") (the incoming order or quote may only trade with another eligible order or quote originating from Another CBSX Trader if the order or quote originating from Another CBSX Trader is at as good a price as the order or quote from the Same CBSX Trader that is being "skipped over").  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 Another CBSX Trader, and any remaining portion thereof will remain in 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 another order to buy 500 shares @ $19.99 from Another CBSX Trader resting behind it.  The incoming sell market order for 500 shares would not trade with the order to buy 500 shares @ $20.00 from the Same CBSX Trader and would also not trade with the order to the originating CBSX Trader.  The resting buy order for 500 shares @ $20.00 remains on the CBSX Book. Cancel Both. If a CBSX Trader has made the election for the Cancel Both 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.  When a CBSX Trader submits an incoming order or quote that would trade against opposite side resting interest from the Same CBSX Trader, that opposite side resting interest will be canceled.  The incoming order or quote (or any portion thereof) will be canceled back to the Same CBSX Trader if such order or quote (or part of such order or quote) cannot trade with another eligible order or quote originating from Another CBSX Trader.  In the case of an opening or re-opening, both of the two orders or quotes will be canceled. Cancel Both Example 1: With your permission, we'll stop right here.  The rule filing seems like a bowl of spaghetti - it never ends.  And it's highly technical in nature.  Compliance Insights recommends that it would be best for interested persons to continue reading about the new proposed order type in the rule filing.  The link is just below. For further details, go to:  [CBOE Rule Filing 12-13, 4/11/12].