Context Navigation

Changes between Initial Version and Version 1 of Ticket #19523, comment 9

initial	v1
1	1	I'm not sure that this would be a good interface. It would allow to add variables, but only variables with default settings (continuous, lower bound 0, no upper bound, no name).
2	2	I think it's better to raise an error, which could help spot programming mistakes -- at least when there's a dimension mismatch between the two problems.
	3	This bound checking should be done by the backends -- see #10232.