An InterplEnv is a specification for a segmented envelope. InterplEnvs can be used both server-side, by an IEnvGen within a SynthDef, and clientside, with methods such as at. An InterplEnv can have any number of segments. An InterplEnv can have several shapes for its segments.
InterplEnvs do not have release or loop nodes. They are of a fixed duration. Mostly, it is meant to be used with IEnvGen, where 'times' are actually an index into the envelope shape.