As others have pointed out, automatic numbering is nicely taken care of through the built-in DisplayFormulaNumbered
style. Custom numbering (both a separate counter and counting sequence) can be introduced into stylesheets, for example, I have made a Theorem
style before.
However, for a one off equation numbers / labels, like the $\LaTeX$ \tag
option, you just want to manually set the CellFrameLabels
option. This can be done using the option inspector or by using CellPrint
or Show Expression. For example
CellPrint[Cell[BoxData[
FormBox[RowBox[{"a", "+", "b", "=", "c"}], TraditionalForm]],
"DisplayFormula", CellFrameLabels -> {{None, "(1a)"}, {None, None}}]]
produces
selecting the cell and looking at the option inspector shows you
how you could edit this option with a GUI:
However, referring to that equation using the standard CellTags and Automatic Numbering / CounterBox combination seems to be a bit tricky...
There might be a nice way of doing it, but nothing immediately comes to mind.
CellLabel
gets close but asRight
is not a valid setting forCellLabelPositioning
it cannot, AFAIK, be made to look as you show. $\endgroup$