@ACTIVITY
#SEE SYSTEMACTIVITY
@ANY
The "ANY" clause is not implemented in the PEW.
@ATTACH
The "ATTACH" statement attaches two specified interaction points, which
must have the same channel types and identical roles. "ATTACH" statements
are used to extend the connection of interaction points down the process
hierarchy. At the lowest level we have connection endpoints; this is where
interactions output through the opposite connection endpoint are queued.
The first interaction point in the "ATTACH" statement must be external,
while the second must be a child external interaction point. Either of
these may already have been bound, by an action of the parent in the first
case, and an action of the child in the second.
@BODY
The keyword "BODY" identifies a module body definition. These definitions
specify module bodies and associate them with module headers.
@BY
#SEE CHANNEL
@CHANNEL
The keyword "CHANNEL" identifies a channel definition. Each channel definition
consists of the channel identifier, its two roles, and the lists of
interactions that may be sent "BY" interaction points associated with each
role.
@COMMON
#SEE QUEUE
@CONNECT
The "CONNECT" statement connects two specified interaction points, which
must have the same channel types and opposite roles. A process may not
connect an interaction point that it has alrady bound. After connection,
any interactions output through one of the interaction points is received
at the other (or its descendant if it is attached). Interactions are
queued according to the queueing discipline of the receiving interaction
point.
@DEFAULT
The DEFAULT statement allows the default queue discipline of all queues that
are not explicitly attributed to be specified. Allowed queue disciplines
are COMMON and INDIVIDUAL.
@DELAY
The "DELAY" clause specifies time constraints for a transition. A "DELAY"
clause may take either one or two arguments. The first argument specifies
the minimum amount of time that must elapse before the transition may be
executed, while the second argument, if present, specifies the maximum
amount of time the transition can be enabled before it MUST be executed.
If no second argument is given, it is assumed to be the same as the first
argument. The PEW deals with the two argument case by selecting some time
in between the two after which the transition will be executed.~
The arguments should be integer expressions; however the second argument may
be an asterisk '*' indicating that the transition has no upper bound on its
execution time.~Note that standard Estelle specifies that "DELAY" and "WHEN"
clauses cannot both occur in a single transition; the PEW does not enforce
this constraint. Instead, the combination is treated as follows: the "WHEN"
clause must be continuously satisfied for the duration of the delay for
the transition to be executed. If at any stage during the delay the "WHEN"
clause is no longer satisfied, the delay timer associated with the transition
is reset.

@DETACH
A "DETACH" statement must be followed by a child external interaction point
or internal interaction point identifier. The module executing the "DETACH"
must be the same module that attached the interaction point. The result
of a "DETACH" statement is that the interaction point and the one to which
it is attached are unbound.
@DISCONNECT
A "DISCONNECT" statement must be followed by a child external interaction
point, internal interaction point, or module variable identifier. The
interaction point (or all external interaction points if a module variable
was specified) and the one to which it has been connected are unbound.
@EXPORT
The keyword "EXPORT" identifies the start of a set of variable declarations
that are accessible by the parent of a module as well as the module
itself. The parent must qualify references to exported variables of
children by preceding them with the name of an appropriate module variable.
Only normal PASCAL variables may be exported.
@EXTERNAL
EXTERNAL procedures and functions are not implemented in the PEW.
@FROM
A "FROM" clause specifies the control states from which a transition may be 
validly executed. Thus the "FROM" clause is part of the enabling conditions
of a transition. The identifiers listed in a "FROM" clause need not be
distinct, and may be any mix of state and state set identifiers. The
abscence of a "FROM" clause implies that a transition may be executed
regardless of the control state.
@HOURS
#SEE TIMESCALE
@INDIVIDUAL
#SEE QUEUE
@INIT
The "INIT" statement creates an initialises a module instance. It specifies
a module variable, body identifier, and actual parameter list. An instance
of a module of the appropriate body type is created, with the external
visibility specified by the type of the module variable. The actual
parameters are passed to this module instance, and a transition from its
initialisation part, if any, is executed. The module instance is then
associated with the module variable.
@INITIALIZE
The INITIALIZE section of a module specifies a set of transitions that may
be selected from when an instance of the module is created with an INIT
statement. At most one of the (enabled) initialisation transitions will
be nondeterministically selected for execution. Initialisation transitions
may contain only TO and PROVIDED clauses.
@IP
The IP keyword specifies the start of interaction point declarations. Each
IP declaration consists of a list of identifiers followed by their type.
The type of an IP consists of (an array of) the associated channel, role,
and optional queue discipline.
@MICROSECONDS
#SEE TIMESCALE
@MILLISECONDS
#SEE TIMESCALE
@MINUTES
#SEE TIMESCALE
@MODULE
The MODULE keyword specifies a module header definition. Module headers
specify the external visibility of modules. The information required to be
specified is the module class, initialisation parameters, external
interaction points, and exported variables.
@MODVAR
Module variables identify instances of modules. The "MODVAR" keyword 
identifies the start of a set of module variable declarations. These
are similar to normal variable declarations, but the type identifiers must
be module header identifiers. When a module variable is initialised it will
be bound to a module body type.
@NAME
The "NAME" construct is used to specify an optional name for a state
transition. These names serve no purpose other than aiding readability,
and are ignored by the PEW.
@OUTPUT
An output statement specifies an interaction point, interaction identifier, 
and actual parameter list. The interaction specified by the interaction 
identifier, together with its parameters, is appended to the reception
queue of the connection endpoint of the specified interaction point.
@PACKED
Packed data types are not implemented in the PEW.
@PRIMITIVE
PRIMITIVE procedures and functions are not implemented in the PEW.
@PRIORITY
A "PRIORITY" clause orders transitions with respect to priority constants.
Priority constants must be positive integers, with zero having the
highest priority. The priority is used by the scheduler when selecting
which transitions to fire from the set of enabled transitions.
@PROCESS
#SEE SYSTEMPROCESS
@PROVIDED
The "PROVIDED" clause is part of the enabling condition of a transition.
It is satisfied if the Boolean expression foolowing the keyword "PROVIDED"
evaluates to TRUE. A special case, "PROVIDED OTHERWISE", evaluates to TRUE
if all provided clauses in the same transition group that lie between this
clause and the previous "PROVIDED OTHERWISE" clause (if any) evaluate to
FALSE. 
@QUEUE
Queue disciplines specify whether or not the queue can be shared by more
than one interaction point. COMMON queues may be shared, but INDIVIDUAL
queues may not.
@RELEASE
The "RELEASE" statement releases module instances at a lower hierarchy level.
Firstly, all external interaction points of the module specified by the
module variable following "RELEASE" are detached or disconnected, and then
the module and all of its descendants are released and are no longer
available. The value of all module variables which identified the released
module are undefined, as though they were never initialised.
@SAME
#SEE TO
@SECONDS
#SEE TIMESCALE
@SPECIFICATION
A "SPECIFICATION" is an Estelle program. The specification should have a
name, a class ("SYSTEMPROCESS" or "SYSTEMACTIVITY"), an optional  default
queue discipline, optional timescale, a number of declarations and
definitions of different objects, a set of zero or more initialisation
transitions, and zero or more body transitions.
@STATE
If the control state space of the EFSM of a process is nonempty, it must
have all of its possible states enumerated in a state definition part.
@STATESET
State sets provide a means of referring to several states at once. A state
set is defined in the state set definition part, and is merely a shorthand
notation for the list of its elements.
@SYSTEMACTIVITY
The classes "SYSTEMACTIVITY" and "ACTIVITY" specify modules that can parent
ACTIVITY children only. (System)activities allow for nondeterministic
sequential execution. When a (system)activity module offers no transitions for 
execution, but its children do, then only one child is selected 
(nondeterministically) for execution. The difference between systemactivities
and activities is that systemactivities are all created as part of the
initialisation of the specification, whereas activities may be freely
created and destroyed at any stage. Other valid attributes are "PROCESS",
"SYSTEMPROCESS", and unattributed.
@SYSTEMPROCESS
The classes "SYSTEMPROCESS" and "PROCESS" specify modules that can parent
both PROCESS and ACTIVITY children. (System)processes thus allow for
synchronous parallel execution. When a (system)process module offers no 
transitions for execution, but its children do, then all of the transitions 
offered by the children that are selected for execution are executed.
The difference between systemprocesses and processes is that systemprocesses
are all created as part of the initialisation of the specification, whereas
processes may be freely created and destroyed at any stage. Other valid
attributes are "ACTIVITY", "SYSTEMACTIVITY", and unattributed.
@TIMESCALE
The TIMESCALE of a specification specifies the implementors intentions as
to what units of time the numbers used in delay clauses are meant to
specify. The timescale has no semantic effect on the program. Valid
timescales are HOURS, MINUTES, SECONDS, MILLISECONDS and MICROSECONDS.
@TO
A "TO" clause specifies the next state following the execution of a state
transition. If there is no "TO" clause, or the state identifier in the "TO" 
clause is "SAME", then the state does not change.
@TRANS
The TRANS section of a module specifies the body transitions for that module.
At each iteration, the clauses of each transition of each active instance of
the module are evaluated, and may be selected for execution, depending on the
class of the module instance and its parent.
@WHEN
A "WHEN" clause is part of the enabling condition of a transition. It should
specify an interaction point and interaction identifier, separated by a
period.  The interaction identifier may be followed by an optional argument
list. A "WHEN" clause is satisfied if the interaction at the head of the
specified interaction point corresponds to the interaction identifier. The
interaction is dequeued only as part of the execution of the transition. In
standard Estelle, a "WHEN" clause cannot be used in the same transition as
a "DELAY" clause, but this is not enforced by the PEW.