You can insert a horizontal line into your topic by clicking the tool button or the down arrow button next to the Variable button and selecting the Horizontal line... menu option or use Ctrl+Shift+H shortcut.
Dr.Explain displays the following dialog:
Width value measurement
Specify the measurement for the line width here: either in % or pixels.
This parameter specifies where the next line should appear in a browser after the line break created by this element. This attribute takes into account floating objects (images, tables, etc.).
Possible values:
none: the line will be drawn normally (default value);
left: the line will be drawn below any preceding float-left objects;
right: the line will be drawn below any preceding float-right objects;
both: the line will be drawn below any preceding float objects.