The header field in your profile is so that you can create post layouts. It is not a second signature going above your post. If you put plain text there, I will blank your layout, just as I would if you had a really ugly layout but actually tried. In general this has been an implicit rule. It definitely used to be explicit, but I guess it was never said anywhere here, but still it's common sense. There's varying levels of bad when it comes to plain-text headers, but they're definitely all quite bad.

I bring this up because one user in particular (I won't name names) keeps on putting up a new and worse plain-text header every time I delete his old one. Perhaps a reasonable person might thing "Hmm, this keeps getting deleted, I wonder if there's some reason for this" but no, this fellow has not thought this.

So yeah, if your plain-text header gets deleted, this is why.

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Pay attention. This will be on the test.