private void RedSelection(int index, int length)
{
if (!txtEdit.Enabled)
return;
// numbers in articleText and txtEdit.Edit are offset by the number of newlines before the index of the text
int newlinesToIndex = WikiRegexes.Newline.Matches(txtEdit.Text.Substring(0, index)).Count;
int newlinesInSelection = WikiRegexes.Newline.Matches(txtEdit.Text.Substring(index, length)).Count;
txtEdit.SetEditBoxSelection(index - newlinesToIndex, length - newlinesInSelection, false);
txtEdit.SelectionBackColor = Color.Tomato;
}