Currently the Z-order of chart objects (which objects being displayed in front of the other) cannot be controlled. This interfere the visibility (and readability) of a Screen Label or Text object if there is a Vertical Line on chart, as the Vertical Line is displayed on top of the label/text.

The requested implementation could change this and the user would be able to select which object (the line or the text in the given example) does he want to display on top.