HACKER Q&A
📣 isoprophlex

Why doesn't HN scrub this train emoji?


See: https://news.ycombinator.com/item?id=28633934

I came across this post that accidentally contains a train emoji. Copy/pasting into a new post worked, even though I thought emoji were scrubbed from submitted text. And indeed when I select a train emoji on my phone keyboard... no trains!

I can't figure out what makes the train in that post special, does anyone know what's going on here? User Zokier mentions "private area unicode" but I'm having a hard time grokking how that causes this issue.

Train from post: 

Train from my phone keyboard: Gets redacted

  👤 chrismorgan Accepted Answer ✓
It’s not a defined emoji. In fact it’s not a defined code point. Private Use Area means that it is specified as having undefined semantics and you can use it for whatever you like. You just happen to have a font that puts a train glyph there. For me, I see a box containing the characters “E01F”, corresponding to the scalar value U+E01F.

https://en.wikipedia.org/wiki/Private_Use_Areas

It would probably make sense for HN to strip out PUA stuff, given its decision to strip emoji.

👤 db48x
Characters in the Private Use Area do not have any predefined meaning. You happen to have a font which shows a train when those characters are used, but most people do not.