A SpecFrame is a specialised form of one-dimensional Frame which
represents various coordinate systems used to describe positions within
an electro-magnetic spectrum. The particular coordinate system to be
used is specified by setting the SpecFrame's System attribute (the
default is wavelength) qualified, as necessary, by other attributes
such as the rest frequency, the standard of rest, the epoch of
observation, units, etc (see the description of the System attribute
for details).
By setting a value for thr SpecOrigin attribute, a SpecFrame can be made
to represent offsets from a given spectral position, rather than absolute
spectral values.