What's the definition of ACTL?

Question

I have been looking for the definition of ACTL, but Google has given me very little to go with.

So far, I know ACTL is another form of CTL model checking, and CTL includes the following operators:

• Always
• Exist
• Global
• Finally
• Next
• AND / OR
• NOT

So what does ACTL include and how is it different from CTL?

Many thanks