Zero-width and invisible
INVISIBLE SEPARATOR (U+2063)
The invisible comma: the separator between the indices in a subscript like aij.
- Codepoint
U+2063- Category
- Zero-width and invisible
- Removed by default
- Yes
- Governing option
- No option needed
- Can be load-bearing
- No
Where it comes from
Equation editors and MathML. In the wild it also shows up in text pasted out of scientific PDFs and from spreadsheet formula bars.
Why it matters
Another invisible codepoint that reads as nothing and compares as something. It is popular in zero-width steganography for the same reason as its three neighbours.
Before and after
Two invisible commas separate three symbols that look like one word.
The character is shown as a labelled chip so you can see where it sits. In your text it draws nothing at all.
When it is legitimate
Inside a real subscript index list in MathML.
How to remove it
The default pass removes it. If the subscript structure matters, keep the MathML source and clean only the text you export from it.
Is it an AI watermark?
Used to hide data — not a watermark
No. It is one of the four invisible maths operators, used by hidden-payload tools as a convenient alphabet. No model emits it as a mark.
A known carrier for deliberately hidden payloads. Someone put it there on purpose, which is a different question from who wrote the words.
Questions
Why not use a real comma?
Because the rendered formula should show "aij" while the underlying structure still knows there are two indices.
What does it do in plain text?
Nothing visible. It only makes two identical-looking strings compare unequal.
Check your own text
Paste anything into the cleaner to see every hidden character it contains, with position, codepoint and what happens to each one. Nothing is uploaded.