Github Markdown has strikethrough support like this:
~~deleted text~~
This would be extremely useful on my site. Additionally, it is sometimes useful to strikethrough an entire paragraph. Maybe it could be implemented like this?
~~~
Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text. Long paragraph of deleted text.
~~~
Additionally, it would be nice to have underline support like Textile:
+underlined+
I know that Discourse has bbcode support too, but I hate bbcode and all [hate]tags[/hate] pretty much.
Markdown suggestions should be directed to talk.commonmark.org, or more specifically this existing thread about the strikeout feature. If Discourse invents its own conventions, that would defeat the whole purpose of creating the CommonMark spec.
The <s> element represents contents that are no longer accurate or no longer relevant.
NOTE: The s element is not appropriate when indicating document edits; to mark a span of text as having been removed from a document, use the del element.
The del element represents a removal from the document.
Using <del> also causes rise for people to use <ins> to insert text, the underline text on the first line of this post is inserted like this: <ins> now available!</ins>