How do i write pickup messages, obituaries, and tags for a custom monster/weapon

I have created some new weapons and monsters, how can I write a custom pickup message, a tag (and what do they do anyway?), and an obituary?

Use the following actor properties in DECORATE:

http://zdoom.org/wiki/Actor_properties#Obituaries
http://zdoom.org/wiki/Actor_properties#Inventory.PickupMessage

Examples:

actor MyMonster {
  Obituary "some text"
}
actor MyWeapon {
  Inventory.PickupMessage "some text"
}

As for tags: If you are talking about the actor property named "Tag", those do exactly what it says on the wiki, and you generally don't need to set them at all. If you are talking about thing tags that you can set in a map editor in Hexen map format or in UDMF, those are used to identify the particular tagged things to be possibly later affected by Action Specials called from ACS, linedef triggers, etc.

Thank you! and I was referring to the actor property, which, as I'm looking at it on the wiki, I must ask why this is in ZDoom? I understand that ZDoom is meant to have support for all doom engine games, but frankly I'm sure that there is a dedicated strife remaster or source port of some kind, and why do doom weapons have tags?

doom weapons have tags in zdoom because of the option that allows you to see inventory's name tags when cycling through them