How does parry work?

[WCW]

The Duelist has the ability to parry attacks for themselves or nearby ally. Does anyone know the actual mechanics of this ability? It does not seem to show the missing attack on the character sheet. Can you do both types of parries (self and ally) together, does it actually work? Does parry use your attack with the highest attack automatically? Do you know if you can make multiple riposte attack of opportunities in one turn? Have you found this to be effective in game?

Description of Parry
"At 2nd level, a duelist learns to parry the attacks of other creatures, causing them to miss. Whenever the duelist takes a full attack action with a light or one-handed piercing weapon, she can elect not to take one of her attacks. At any time before her next turn, she can attempt to parry an attack against her or an adjacent ally as an immediate action.
To parry the attack, the duelist makes an attack roll, using the same bonuses as the attack she chose to forego during her previous action. If her attack roll is greater than the roll of the attacking creature, the attack automatically misses. For each size category that the attacking creature is larger than the duelist, the duelist takes a –4 penalty on her attack roll. The duelist also takes a –4 penalty when attempting to parry an attack made against an adjacent ally."

Description of Riposte
"Starting at 5th level, a duelist can make an attack of opportunity against any creature whose attack she successfully parries, so long as the creature she is attacking is within reach."

[hilburnashua]

Haven't ever played a duelist in Kingmaker/Wrath so I don't know for certain, but I imagine it is another ability you can turn on at the start of your turn that causes you to loose your lowest base attack. Then the first time conditions are met, the ability triggers. You don't actually get to "choose" to use it. IE, you won't get a popup window asking if you want to use parry.