In an EBIF resource, programmatic (procedural) information takes the form of byte code, where each operation and its (optional) operands is referred to as an action. Actions are organized into sequences by means of one or more action tables where each entry points at (1) an encoded action and (2) the action table index of the next action to execute after the current action's execution is completed. An action sequence terminates when the next action table index is a special value (0xFFFF) or in the case of certain flow of control actions. Action sequences effectively represent one or more traditional code blocks with potential internal looping behavior.
Action sequences are executed as a result of firing certain predefined events, such as a page load event, a key press event, a click event, etc. As such, all programmatic execution takes place in the context of event handlers, whose execution is serialized by an ETV User Agent.
The following categories of actions are defined by EBIF:
- Flow of Control Actions
- Predicate Actions
- Variable Store Actions
- Arithmetic Actions
- Boolean Logic Actions
- Mathematic Actions
- String Actions
- Array Actions
- Application and Page Actions
- Widget Actions
- Table Actions
- Miscellaneous Actions
Memory Model
The action memory model is based on a variable store, and does not make use of registers or a stack. With the exception of one predefined, internal result value variable, all variables are preallocated (and typed) at compilation time. These variables are represented in the form of a table referred to as an augmented reference table, where the content of the table is initialized at compilation time, then stored and mutated at runtime by an ETV User Agent.
Execution Model
The action execution model is based on the decoding and processing of action sequences that serve as event handlers.
Execution of action sequences are serialized through the sequential dispatching of events to event handlers, completing the execution of an action sequence functioning as an event handler before executing any other applicable event handlers (for that event) and before processing any other enqueued event.