SanitiseHtml() removing content

[donaldgray]

The following test passes:

const string input = "<p><strong>Sample</strong></p>text<ul><li>One</li><li>Two</li><li>Three</li></ul>";
const string expected = "<span><p></p>text</span>";

var actual = input.SanitiseHtml();
actual.Should().Be(expected);

but it is removing all content within the <ul> and <strong> tags, rather than just the tags themselves.

This method is to handle html as per https://iiif.io/api/presentation/3.0/#45-html-markup-in-property-values - should the content be left as-is but tags removed? Or does it make sense to remove content too?