From an answer to Keyboard entry of square bracketed matrices in text cells, How to? ,
I cribbed this code:
CurrentValue[EvaluationNotebook[], InputAliases] = DeleteDuplicates@ Append[CurrentValue[EvaluationNotebook[], InputAliases], "bmat" -> RowBox[{StyleBox["[", SpanMaxSize -> Infinity], GridBox[{{"\[SelectionPlaceholder]", "\[Placeholder]"}, {"\[Placeholder]", "\[Placeholder]"}}], StyleBox["]", SpanMaxSize -> Infinity]}]];
It works OK, but sometimes Mathematica delets the SpanMaxSize directive when automatically reformatting. There may be a way to prevent that, but (I think) I would prefer that square brackets acted the same as parentheses, by default. Is there a way to make that happen?
Am I likely to regret doing so? That is, is there some compelling reason that square brackets (or curly brackets) are not "stretchy" by default?
Version 10.4.0 for Microsoft Windows (64-bit) (February 26, 2016)
Edit to add image showing surprising consequence of getting what I asked for. Not a show stopper, but ...