In some cases it is desired to customize the empty cell of a reference or child cell but still retain the behavior of the cell to completely be replaced by the first character the user types.
To customize the empty cell of such a cell, usually the editor DSL provides a field labeled /empty cell. For some cell types this must first be enabled by setting customize empty cell in the Inspector to true.
However, when you just enter any constant here, the behavior of cell is not the same as the default empty cell.
To achieve the desired behavior of completely being replaced by the first character, use the text* aka nullText property of the constant cell instead of the text property (see bottom of Inspector).
When looking deeper into why and how this works, the actual behavior depends on whether the text is set via EditorCell_Label.setText(String) or via EditorCell_Label.setDefaultText(String) with any non-empty string being set via setText hiding the "default" or "null" text.
The CellModel_Constant basically just calls setText with the value of text and setDefaultText with the value of text* aka nullText (this is done in the generator).
The error cell (both variants described in Error Cells) also uses this technique to achieve the same behavior.
However, it decides to which method to give its text based on its myEditable flag in its synchornizeViewWithModel method.
To actually look exactly like the default empty cell, I've found that the following styles must be set:
EmptyCell {
font-style : bold
}
with EmptyCell from BaseLanguageStyle from jetbrains.mps.baseLangauge.editor