Subject: Re: bug#73862: [PATCH] Add `header-line-active` and `header-line-inactive` faces.

From: Eli Zaretskii <[email-masked]>
Date: Mon, 09 Dec 2024 05:26:34 +0200

> From: Eshel Yaron <[email-masked]>
> Cc: [email-masked],  [email-masked],
>   [email-masked],  [email-masked]
> Date: Sun, 08 Dec 2024 21:56:33 +0100
> 
> Aaron shared a recipe to reproduce this behavior, copied here:
> 
> --8<---------------cut here---------------start------------->8---
> (setq header-line-format "Some header")
> (face-remap-set-base 'header-line 'highlight)
> (switch-to-buffer-other-window "new")
> ;; In new buffer/window:
> (setq header-line-format "Some header")
> (other-window 1)
> ;; In original buffer/window:
> (set-face-attribute 'default nil :height (+ (face-attribute 'default :height) 10))
> --8<---------------cut here---------------end--------------->8---

Are you also change the attributes of the default face to cause the
"spreading"?  If not, please show a recipe.  Because I was unable to
see this without something like the last line of the recipe, and also
that line _must_ be in the buffer where header-line is remapped,
otherwise the effect is not seen.