Highlight cells selected feature : Request?

Question

I always delete more cells than I want to. This is because every time I choose the cells, I am not looking at the corresponding code belonging to that cell bracket (why? because Mathematica doesn't highlight what I am selecting). When you have multiple lines of code (single-celled) and you want to delete some at a stretch, you may accidentally delete one which you dint want to.

Is there an option in v.11 ? Or is this a feature that must be requested. Irrespective of all these, this should be a default feature.

1 Highlights cell brackets, but not cell: 2 Different FONT STYLE with cut+paste on same notebook

Answer 1

So I disagree that this should be a default feature (I think it would interrupt my flow, at least). But it's not so tough to get this in as a default feature.

If you only want it to affect your notebooks going forward, you can make your own stylesheet where you implement this and then set:

CurrentValue[$FrontEndSession, DefaultStyleDefinitions]

to that stylesheet.

Alternatively we can take advantage of the fact that FrontEnd`FindFileOnPath will scan $UserBaseDirectory before the system dirs.

That means we can make a whole-sale copy of "Default.nb" in the $UserBaseDirectory and just muck-about with that:

$userBaseStyles =
  FileNameJoin@{
    $UserBaseDirectory,
    "SystemFiles",
    "FrontEnd",
    "StyleSheets",
    "Default.nb"
    };
With[{defStyles = 
    FrontEndExecute@
     FrontEnd`FindFileOnPath["Default.nb", "StyleSheetPath"]},
  CopyFile[defStyles, $userBaseStyles]
  ];
SetOptions[
 NotebookOpen[$userBaseStyles],
 {
  Editable -> True,
  Saveable -> True
  }
 ]

There should then be a way to add in your defintion. Here's a first guess, although it should be possible to do this with things in the FEPrivate` context. (when I figure that out I'll post it)

Update: FEPrivate confusion

by what I know about the FEPrivate` context this ought to be working:

FEPrivate`If[
 FEPrivate`MemberQ[
  FrontEnd`Cells[
   FrontEnd`NotebookSelection[FrontEnd`InputNotebook[]]
   ],
  FrontEnd`EvaluationCell[]
  ],
 Hue[.6, .05, 1],
 Inherited
 ]

But for reasons I don't understand it is not. Obviously it doesn't work with FE`Evaluate, because neither FronEnd`Cells nor FrontEnd`EvaluationCell work with it, but I thought in the past it had resolved such things fine, anyway.

Original:

FontColor -> 
 Dynamic[If[MemberQ[SelectedCells[], EvaluationCell[]], Blue, 
   Inherited]]

To the cell using Command-Shift-E (on Mac) or Cell > Show Expression

Then restart and you have your change.