fix: hide the header in the iframe on documentation page

Author: julhoang

core/htmlhelper.py

@@ -176,7 +176,10 @@ def modernize_legacy_page(
     """Modernize a legacy Boost documentation page."""
     HIDE_TAGS_BASE = []
     if not show_navbar:
+        # Legacy navbar
         HIDE_TAGS_BASE.append(("div", {"class": "header-menu-bar topnavbar"})),
+        # V3 navbar
+        HIDE_TAGS_BASE.append(("header", {"class": "header"}))
 
     if soup.html is None:
         # Not an HTML file we care about

templates/v3/includes/_header_v3.html

@@ -16,6 +16,10 @@
 
   Usage:
     {% include "v3/includes/_header_v3.html" %}
+
+  Note: This header is also rendered inside the iframe on the doc page and is
+  hidden there by core/htmlhelper.py. If you change the .header class name,
+  update the matching HIDE_TAGS_BASE entry in core/htmlhelper.py.
 {% endcomment %}
 <header class="header">
   <div class="header__inner">