Blurb:: Sequence of expansion orders used in a multi-stage expansion

Description::

Each level entry of the \c expansion_order_sequence applies to one
expansion within a multi-stage expansion.  Current multi-stage
expansions that support expansion order sequences include multilevel
or multifidelity polynomial chaos.

If adaptive refinement is active, then this sequence specifies the
starting point for each level within either an individual or
integrated refinement approach.

A corresponding scalar specification is documented at, e.g.,
\ref method-polynomial_chaos-expansion_order

Topics::
Examples::
Theory::
Faq::
See_Also::	method-polynomial_chaos-expansion_order
