1
Several years ago, there was a post on this site that probably answers your question. Unfortunately, I did not record the author or the title of that post. Within the approach of that old post a palette is created to insert all possible pairs of parentheses. Below I reproduce the code from that post:
CreatePalette[
Column[{Style[
Grid[Join[
...
1
This works on DisplayFormula cells and satisfies all three requirements. Hope this helps.
CreatePalette[{
Button["Insert Alignment Marker",
NotebookWrite[InputNotebook[], "\[AlignmentMarker]"]],
Button["Turn on Alignment",
SelectionMove[InputNotebook[], All, Cell];
SetOptions[...
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