@specified_duration(string)
@specified_duration(exe)
@specified_duration(proc)

returns in the specified duration of the argument. The argument must refer to a musical event (through its label) or to an action (through its label, an exe or the name of a proc). The specified duration, expressed in beats, is:

Notice that, for a loop, the specified duration is not linked to its period. Note also that the specified duration of an exe is the specified duration of the compound action that instantiate into this exe. So, a specified duration is a static notion, refering to the score, not to runtime values.

The specified duration can be computed (statically) only if the delays of the involved actions are given statically (as constant) in beats. If this is not the case (some delays are specified in seconds and others in beats, or if delays are expressed by an expression), then @specified_duration returns -1.

A common misunderstanding is to look for a “dynamic version” of the notion of specified duration, for instance to take into account delays expressed by an expression. Such thing cannot be computed in the general case because the value taken by a delay expression in the futur cannot be computed in the present (causality). If the objective is to trigger some action at the end of a compound action, cf. continuation operators.