Commands that also require variables only known at run0time in the sequencer
should implement this interface to be rendered successfully. A prominent
example would be a target that requires a filter sequence like
VRI and defines so in a setup. Depending on the loop counter in the
sequence, the current active filter can be derived.
Registers the sequencer variables as a lookup table from name to value
as provided by the sequencer. Currently, the loopcounter
Sequenceloop and the looptime Sequencetime
are known, but may change in the future.