When manually placing a dimension gap symbol (a symbol that creates a small break in a dimension line), it can be difficult to get the proper placement because the gap symbol has no visible geometry and therefore gives no useful feedback during the placement process. However, if you move the symbol after placing it (as you will likely need to), a small, temporary rectangle is drawn (overlay graphics) to show the outline of where the gap will be placed. Why the rectangle isn't shown when initially placing the symbol seems to be a bit of an oversight - one that we can correct with a bit of code.