Unicode includes six "zero-width characters" that are not visibly rendered in browsers (U+FEFF, U+200C, U+200D, U+200E, U+2060, U+180E) — they're used for some specialized cases in rendering non-Roman alphabets.
Inzerosight's browser extension allows you to insert and detect hidden messages encoded in zero-width characters; absent the plugin or a source-code inspection, these do not show up at all, not even when the text is highlighted.
I may or may not have included some of this text in this post.
inØsight [Planetrenox]
(via Hackaday)
