Terms and Definitions

For the purposes of this document, the following terms and definitions apply:

a value passed to a function, that is intended to map to a corresponding parameter.
external appearance or action.
behavior, implementation-defined
behavior specific to an implementation, where that implementation must document that behavior.
behavior, undefined
behavior which is not guaranteed to produce any specific result. Usually follows an erroneous program construct or data.
behavior, unspecified
behavior for which this specification provides no requirements.
restriction, either syntactic or semantic, on how language elements can be used.
error, fatal
a condition in which the engine cannot continue executing the script and must terminate.
error, fatal, catchable
a fatal error that can be caught by a user-defined handler.
error, non-fatal
an error that is not a fatal error and allows for the engine to continue execution.
an expression that designates a location that can store a value.
lvalue, modifiable
an lvalue whose value can be changed.
lvalue, non-modifiable
an lvalue whose value cannot be changed.
an informational message informing user of the code that may not work as intended.
a variable declared in the parameter list of a function that is intended to map to a corresponding argument in a call to that function.
PHP Run-Time Engine
the software that executes a PHP program. Referred to as the Engine throughout this specification.
a primitive unit of data operated by the Engine having a type and potentially other content depending on the type.

Other terms are defined throughout this specification, as needed, with the first usage being typeset like this.