What is ! modifier for?

[TeamGrizzly]

Saw some macros like /cast !Rune Strike. What is the purpose of the ! modifier?

[Legendary]

It's used for 'on next strike' abilities. Pretty much stops you from hitting the key twice and turning off the ability.

[Siaea]

It makes it "on" no matter how many times you spam the key.

[Ualaa]

I have a pally macro:

/cast [mounted] !Crusader Aura; [nomounted] !Devotion Aura

The !'s make it spammable.
The Crusader Aura or Devotion Aura is run only once.
And even on later presses, will not run.
So it won't turn off, on a second click.

Naturally, changing from on foot to mounted.
And the other spell will run once.

[Maxion]

I have a pally macro:

/cast [mounted] !Crusader Aura; [nomounted] !Devotion Aura

The !'s make it spammable.
The Crusader Aura or Devotion Aura is run only once.
And even on later presses, will not run.
So it won't turn off, on a second click.

Naturally, changing from on foot to mounted.
And the other spell will run once.

Nice one, I think i'll add this to my buff button on the pally.

[Boogieman]

I use this for Hunter aspects to make sure they are all in the same aspect
(you can spam it and it wont turn the aspect off)