What is Spell Speed?
Spell Speed refers to how "fast" card effect resolves after activation. There are 3 Spell Speeds:

• Spell Speed 1
  Spell Speed 2
  Spell Speed 3
  

Each Spell Speed can only be countered with one that is greater, or equal. The exception to this is Spell Speed 1, which cannot be used against each other in normal play, unless special situations allow it.

How Spell Speeds work?
Spell Speed 1 < Spell Speed 2 < Spell Speed 3

Summoning a monster and declaring an attack are actions that do not have a Spell Speed, and therefore cannot be "chained" to. However, if the action in question was the last action to have resolved on the field, you may activate a card in response, which then becomes Chain Link 1. For example, using "Bottomless Trap Hole" when a monster is Summoned, or using "Mirror Force" when your opponent's monster declares an attack, and all considered to be "activated in response".

Spell Speed 1 is the only Spell Speed that cannot be countered by cards of the same Spell Speed during normal play.

The following are all Spell Speed 1:
• Normal/Field/Continuous/Equip & Ritual Spell Cards
• Continuous/Ignition/Trigger & Flip Monster Effects


Spell Speed 2 cards can be used against Spell Speed 1 and other Spell Speed 2 cards as well

The following are all Spell Speed 2:
• Quick-Play Spell Cards
• Normal & Continuous Trap Cards
• Quick Monster Effects

Spell Speed 3 cards can be used to counter all the 3 Spell Speed cards. That means Dark Bribe can counter Royal Decree. But of course If Royal Decree is already on the field you cannot activate Traps.

Spell Speed 3 cards can only be countered with other Spell Speed 3 cards.

Therefore, you cannot counter "Negate Attack", "Magic Jammer", "Trap Jammer" or "Magic Drain" with "Royal Decree". That is you cannot Chain Royal Decree to Counter Traps.

The only Spell Speed 3 cards are Counter Traps.