In the campaign both the rebels and the imperials have an ability that triggers upon declairing an attack. In the timing rules it says the attacker's ability triggers first. The in the timing rules for the campaign it says the imperial ability always triggers first.

Which one is it?

RRG Page 2:

Golden Rules

If a rule in this guide contradicts a rule in the Learn to Play

booklet or Skirmish Guide, the rule in this reference guide takes

priority.

RRG Page 2:

Timing

Numerous game effects have the possibility of triggering at the

same time. If this occurs, use the following to determine the order

in which these effects are resolved:

In a campaign, resolve mission rules first, followed by effects

triggered by the Imperial player, then effects triggered by Rebel

players.

In a skirmish, resolve mission rules first, followed by effects

triggered by the player with initiative, then effects triggered by his

opponent.

During an attack, in both a campaign and a skirmish, resolve

mission rules first, followed by effects triggered by the attacker,

then effects triggered by the defender.

For additional information on timing conflicts, see “Conflicts” on

page 9.

RRG Page 9:

Conflicts

Numerous abilities, mission rules, and other game effects can be

triggered at the same time.

• While attacking, mission rules are resolved first, followed by

effects from the attacker (including figures friendly to him), then

effects from the defender (including figures friendly to him).

• Effects from multiple figures under the control of a single

player are resolved in the order of that player’s choice.

• The decision for a player to resolve an optional effect coincides

with the order of resolution. After a player has declined to

trigger one or more abilities, he does not have the opportunity

to trigger that ability until the next triggering instance.

Conflicts in a Campaign

During a campaign, mission rules are resolved first, followed by

effects from the Imperial player, then effects from the Rebel players.

• If multiple mission rules would resolve at the same time, the

Imperial player decides the order of resolution.

• When Rebel players wish to resolve multiple effects at the

same time, they collectively decide the order of resolution.

• If heroes are required to make a decision as a group and

cannot come to a consensus, the Imperial player chooses a

Rebel player to make the final decision.

Conflicts in a Skirmish

During a skirmish, mission rules are resolved first, followed

by effects from the player with initiative, then effects from his

opponent.

• If multiple mission rules would resolve at the same time, the

player with initiative decides the order of resolution.