When a span has nested strikethrough and underline tags applied to it only the inner tag is respected.
This HTML:
<u><del>UnderlineStrikethrough</del></u>
results in:
UnderlineStrikethrough
And this HTML:
<del><u>UnderlineStrikethrough</u></del>
results in:
UnderlineStrikethrough
As a possible workaround, you can add some text placeholder to the span that needs both "underline" and "strikethrough" and after import set the properties, and remove the placeholder text.
Sample HTML:
<u><del>##PlaceholderStart##UnderlineStrikethrough##PlaceholderEnd##</del></u>
after import, execute this:
const string PlaceholderTextStart = "##PlaceholderStart##";
const string PlaceholderTextEnd = "##PlaceholderEnd##";
RadFlowDocumentEditor editor = new RadFlowDocumentEditor(document);
Regex regex = new Regex(PlaceholderTextStart + "[a-zA-Z]*" + PlaceholderTextEnd);
var results = editor.FindAll(regex);
foreach (var result in results)
{
foreach (var run in result.Runs)
{
run.Properties.Strikethrough.LocalValue = true;
run.Properties.UnderlinePattern.LocalValue = Telerik.Windows.Documents.Flow.Model.Styles.UnderlinePattern.Single;
run.Text = run.Text.Replace(PlaceholderTextStart, string.Empty);
run.Text = run.Text.Replace(PlaceholderTextEnd, string.Empty);
}
}