701.7aTo discard a card, move it from its owner’s hand to this player’s graveyard.
The Commander replacement impact changes this is:
To discard a card, move it from the owner’s hand compared to that player’s demand area.
Discard is a search term action that instructs you to move a card from 1 area to another like obliterate, give up, or exile. The action doesn't care if areas of it were changed with other activities, it however happened. Likewise if you have a Dragon Appeasement and give up your commander you get to draw a card.
In addition because the actually being placed into the graveyard is being changed discarding your leader and placing it when you look at the command area wont trigger any "if this card gets in the graveyard from everywhere" triggers like Ulamog, the Infinite Gyre, just like how a sacrificed leader won't trigger any "dies" triggers.
If the adversary discards a card although you control Leyline of the Void, abilities that function when that card is discarded (such Liliana's Caress's capability, or a madness ability of this discarded card) however work, even though that card never achieves that player's graveyard. In addition, means or capabilities that check out the characteristics of this discarded card (including Chandra Ablaze's very first capability) can find that card in exile.