How can I disable text selection using shift without disabling all text selection?

Question

So I know this sounds like a duplicate, but it isn't (or if it is, the accepted answer on all the ones I can find doesn't work the way I need it to). The issue is this:

I'm writing in HTML5 using jQuery, I need to make a grid allow multi-select with control and shift. I have that logic working, but whenever you shift-click it selects the text in the grid. I want to prevent this selection, but here's the critical difference between this and the other questions I found: I want selection of text to work at all other times.

To restate: I want to disable text selection using shift WITHOUT disabling all text selection for the elements specified. Does anyone know how I can do that?

-- EDIT --
The following (in the constructor for the grid) solved this for me. As the answerer suggested, I declared a class for unselectability.

this.gridBody = $("#userGrid");
var handleKeydown = function(e)
{
  e = e || window.event;
  var keyPressed = e.keyCode || e.which;
  if (keyPressed == keys.shift) {
    e.data.gridBody.addClass("unselectable");
  }
};
var handleKeyup = function(e)
{
  e = e || window.event;
  var keyPressed = e.keyCode || e.which;
  if (keyPressed == keys.shift) {
    e.data.gridBody.removeClass("unselectable");
  }
};

$(document).on('keydown', this, handleKeydown);
$(document).on('keyup', this, handleKeyup);

Answer 1

That will bind on document an event where it disables text selection upon pressing DOWN shift

 document.onkeydown = function(e) {
  var keyPressed = e.keyCode;
  if (keyPressed == 16) { //thats the keycode for shift

    $('html').css({'-moz-user-select':'-moz-none',
       '-moz-user-select':'none',
       '-o-user-select':'none',
       '-khtml-user-select':'none',
       '-webkit-user-select':'none',
       '-ms-user-select':'none',
       'user-select':'none'
    }); //or you could pass these css rules into a class and add that class to html instead

    document.onkeyup = function() {
      //here you remove css rules that disable text selection
    }
  }
}

Hopefully i have helped you.

Based on comments

document.onkeydown = function(e) {
  var keyPressed = e.keyCode;
  if (keyPressed == 16) { //thats the keycode for shift

    $('html').addClass('unselectable'); //unselectable contains aforementioned css rules

    document.onkeyup = function() {
       $('html').removeClass('unselectable'); //and simply remove unselectable class making text selection availabe
    }
  }
}