From d77d31ef13ba0e40fbe78e1bbc549fa7ac394074 Mon Sep 17 00:00:00 2001
From: Adrian Chaves <adrian@zyte.com>
Date: Sun, 9 Aug 2026 12:17:34 +0200
Subject: [PATCH] Document lax ID selector syntax as a non-standard extension

---
 docs/index.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/docs/index.rst b/docs/index.rst
index 0f331ab..c86583c 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -124,6 +124,9 @@ be implemented):
 
 These are non-standard extensions:
 
+* ID selectors whose value is not a valid CSS identifier, e.g. ``#37signals``.
+  The specification only allows an identifier after ``#``, so such IDs, which
+  are valid in HTML, would otherwise require ``[id="37signals"]``.
 * The ``:contains(text)`` pseudo-class that existed in `an early draft`_
   but was then removed.
 * The ``!=`` attribute operator. ``[foo!=bar]`` is the same as