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

Description::

Each level entry of the \c start_order_sequence applies to one
expansion within a multi-stage expansion.  Current multi-stage
expansions that support start order sequences include multilevel
and multifidelity function train expansions.

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-function_train-start_order

Topics::
Examples::
Theory::
Faq::
See_Also::	method-function_train-start_order
