XKCD: Invisible Formatting.

Instantly laughing.

That's exactly why I hate WYSIWYG editor. Prefer markdown or similar instead.

Ayam J-Pop : As a perfectionist myself, this issue always concerns me too.

They should make no formatting if it's only empty space character. Or if the tag is empty, then automatically erase the tag.

Sometimes I need to check its source directly to make sure there's no "invisible formatting" in WYSIWYG.

Ayam J-Pop : GitHub, Reddit, SourceForge, all use Markdown or its variants.

Plurk uses basic mark-up formatting like Google+, but better.

This is bold.
This is italic.
This is monospace.
This is strikethrough.
This is a link.

But only that, mostly for text attributes. Basic formatting.

As far as I know, Facebook, Twitter, and Instagram don't have any mark-up formatting (dunno, rarely use tho). But WA also supports basic text formatting mark-up.

Wikicode is too cluttered. LaTeX is the best and the most professional.