Ulven asks via a comment on an older post:

Is it allowed, Midchart, to play 1S as 11-13 balanced? There's a structure I've liked for years:

1C 16+

1D 11-15 unbal w/o 5H

1H 11-15 5+H

1S 11-13 bal

1N 14-16 bal

2C 11-15 minors

This means both weak and strong NT with a lot less risk!

Ulven notes that opening the weak NT (here 11-13) as a suit makes it a lot harder for the opponents to double for big numbers. 

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This is not mid-chart legal.  The change to the mid-chart is: "Any strong (15+ HCP) opening bid" - thus the 1S opening has to be 15+ if artificial. This structure would be allowed:

1C 16+

1D 11-15 unbal w/o 5H

1H 11-15 5+H

1S 15-16 bal

1N 12-14 bal

2C 11-15 minors

Sadly the weak NT has to be opened 1NT.

The 15+ openings require a pre-alert, but no suggested defense - I suggest having one anyway.