underline-style Appearance of the Underline

Style of underline to be used (for example, “single”, “double”, “dashed”).

Usage/Remarks

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.
OPTIONAL on element: <underline>
Value Meaning
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.
Tagged Sample

Requesting underlined text be displayed with a single or double rules

...
<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>
...