The AFL block
introduces a local instance of variable *current-speech-state*. This instance is set to the instance of *current-speech-state* that was referenceable just before execution of the block, and statements are executed within this new local scope. Within the block, all free occurrences of *current-speech-state* refer to the new local variable. Further, this local variable describes the state of the audio formatter, so changes to it immediately affect the voice synthesizer. Upon termination of the block, local variable *current-speech-state* is destroyed, and the audio formatter is reset to its pre-existing state. The programmer has no control over the name of this local state variable and cannot create other local variables using the AFL block.
Execution of statement (terminate-block) causes the currently-executing block to terminate immediately. A browser can execute this statement when the audio rendering of an object is to be terminated prematurely because of an interrupt from the user.
AFL blocks are simpler than the standard block construct provided by full-blown programming languages. For the purpose of audio formatting, where the major task is to control the parameters of the speech space, our experience has shown that the AFL block is more than adequate. Further, our simplified version of the block prevents rendering rules from making changes to the state of the audio formatter that could persist after termination of a block. Such changes, which would be possible with the conventional block, would also complicate the implementation, which has to maintain the connection between the state of local variable *current-speech-state* and the voice synthesizer itself.