The definition should be based on the preceding definition. If this directive is used, all the properties of the previous definition are copied to this one. For the first definition in a file a “Copy” has no effect.

# Apply a weak green glow to Doom's nukage barrel.
Light {
  State = "BAR1";
  Flags = nohalo;
  Color { .2 .4 .22 };
  Size = 0.21;
  Y Offset = -6;
}

# Barrels use two states - copy the previous definition and add a subtle flicker effect.
Copy Light {
  State = "BAR2";
  Size = 0.22;
}

The definition should alter the contents of a previously created definition.

Thing Mods "POSSESSED" {
    Spawn Health = 1000;
}

Presently only Map Info definitions support conditions.

An optional conditional expression can be used to instruct the DED parser to only apply the modification if the expression matches. The expression can be negated using the keyword 'not'.

For example:

Map Info mods "E1M1" if not custom {
     Music = "mysong";
 }