It is possible to set zero width or height for an adornment allowing it to server as a rule or linear divider on a map. Note that such dividers can only be of horizontal or vertical alignment - i.e. not at any angle. It is possible to set both height and width to make a small dot.
The colour of the resulting line is the adornment $BorderColor. If that is left as the default 'automatic' value, then setting $Color for the adornment will give the intended value and may be a more intuitive way of setting it.
The height and or width of a divider is set via its $Border attribute (default =2). Thus, a zero-width adornment will draw as unit wide vertical line of height $Height with a width as if there were a persistent border of $Border value 1. Conversely, setting a wide border value, e.g. 10, causes a 10 wide block of colour. In contrast, a default adornment set 10 units wide would show 6 units width of inner colour and two 2 unit wide borders. Thus a wide border on a zero-width/depth adornment sets a band of solid single colour. If the $Border is set to 0, the adornment renders with an overall width and/or height of 1 pixel in $Border colour.