Unicode tag block, U+E0000 to U+E007F

A block of 128 invisible characters that mirror ASCII. Each one is a copy of a printable ASCII character with no visible form at all, which means an entire readable message can be encoded inside them and hidden in plain text.

How it works

The block from U+E0000 to U+E007F mirrors printable ASCII exactly: U+E0041 corresponds to A, U+E0061 to a, and so on, offset by 0xE0000. Each character has zero width and no glyph. That correspondence is what makes the block usable as a covert channel, since any ASCII string can be re-encoded character by character into tag characters, appended to ordinary text, and carried through anything that copies bytes, with a reader seeing nothing. The block was originally defined for language tagging, was deprecated for that purpose, and retains only one sanctioned use: emoji flag sequences for subdivisions such as England and Scotland, which encode the region code in tag characters after a base flag. Everything else in the block appearing in ordinary prose is either an accident or a payload, and a census tells you which in a second.

What it is legitimately for

Almost none left. The block was deprecated for its original language-tagging purpose, and its only current sanctioned use is in emoji flag sequences for subdivisions such as England and Scotland.

What it breaks

• Text can carry a hidden payload that no reader sees, which is a documented technique for hiding instructions where a human reviewer will not find them.
• The characters travel through copy and paste like any other, so the payload survives into wherever you put the text.

How to find it yourself

A hex dump shows the f3 a0 range. This is the one case where a census is genuinely worth running on text you did not write.

What Clipboard Sanitizer does

Removed everywhere, the entire block.