Pop a Boolean value; if true then jump to the specified action; otherwise continue with the following actions.
There is no Branch If False action. Instead, first use the Logical Not, then Branch If True.
The offset, which is defined in bytes, must be such that when added to the current instruction pointer it points to a valid action (i.e. you cannot jump in the middle of a Push Data or any other such action.)
The offset cannot point outside of the current block of execution, although it can branch to the very end of the block. So if you are inside a With or Try block, a Branch If True cannot be used to exit that block. This can be a problem if you are trying to implement some advanced functionality in an ActionScript compiler such as a goto instruction.