--- "Deathmatch" or "DM" is normally described as any In-Character fight between player characters until death.
When you as your character get injured in-game, you will often only lose health points.
To provide a more immersive roleplay atmosphere to other players, you could and should perform Pain RP with your character's injured body parts, such as showing IC pain or frustration from the injuries, perhaps being knocked to the floor or having trouble using the damaged limb.
In IC chat, you're saying things coming from your character's mouth, not yours.
Naturally you may not use emoticons in this chat (like "XD") or anything similar.
Keeping other knowledge after death is a case of Meta Gaming. --- --- "Voiding" or "Void" is the OOC act of reverting or cancelling IC events due to mistakes.