Appearance of the Underline
Style of underline to be used (for example, “single”, “double”, “dashed”).
This attribute was added to preserve this information when a publisher supplies it. The use of the attribute does not guarantee that the display will produce the formatting requested.
Used on Element: <underline>
|Text, numbers, or special characters||The style of underlining requested; for example, “double” would mean underlined by two rules, very close together.|
|Restriction||@underline-style is an optional attribute; there is no default.|
... <p>In accounting, a single underline denotes a subtotal (e.g., <underline underline-style="single">$483.20</underline>); a grand total is designated by a double underline (e.g., <underline underline-style="double">$1,294.68</underline>).</p> ...