Renders a safe subset of HTML with native controls, as GitHub shows it in a README, without running or fetching anything but images:
href, src, alt, title, width, height, align and
dir attributes are read. Any other tag, and a tag without its match, is dropped, and the text around it
shows; the content of <script> and <style> is dropped too. Part of
UseGitHubExtensions(MarkdownPipelineBuilder, MarkdownExtensionsOptions?) and UseSupportedExtensions(MarkdownPipelineBuilder, MarkdownExtensionsOptions?).
public static MarkdownPipelineBuilder UseHtmlSubset(this MarkdownPipelineBuilder builder)