From 3a5c90f2873116b7948afbb335aec4f816abf8d1 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Fri, 31 Oct 2025 16:48:28 +0100
Subject: [PATCH 1/7] Improve and update the existing Security Considerations -
 fixes #287

---
 index.bs | 503 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 492 insertions(+), 11 deletions(-)

diff --git a/index.bs b/index.bs
index ca53380..374add5 100644
--- a/index.bs
+++ b/index.bs
@@ -1453,10 +1453,15 @@ URLs, is as follows:
 # Security Considerations # {#security-considerations}
 
 The Sanitizer API is intended to prevent DOM-based Cross-Site Scripting
-by traversing a supplied HTML content and removing elements and attributes
-according to a configuration. The specified API must not support
-the construction of a Sanitizer object that leaves script-capable markup in
-and doing so would be a bug in the threat model.
+by traversing supplied HTML content and removing elements and attributes
+according to a configuration. The Sanitizer API ships a strict baseline,
+such that scripting can never be allowed (cf. [[#never-allowed]]).
+In addition to this, a default safe list includes further restrictions that may help
+prevent a wide range of undesirable effects. These include, elements that can override
+site-specific settings (e.g., `<meta>`), embed third-party content or change the
+layout of the page (e.g., `<img>`, `<style>`).
+In addition, we disallow element and attribute configurations that lead to outgoing HTTP
+requests, and form controls. A detailed list is given in [[#default-disallowed-elements]].
 
 That being said, there are security issues which the correct usage of the
 Sanitizer API will not be able to protect against and the scenarios will be
@@ -1466,8 +1471,7 @@ laid out in the following sections.
 
 <em>This section is not normative.</em>
 
-The Sanitizer API operates solely in the DOM and adds a capability to traverse
-and filter an existing DocumentFragment. The Sanitizer does not address
+The Sanitizer API operates solely in the browser. The Sanitizer does not address
 server-side reflected or stored XSS.
 
 ## DOM clobbering ## {#dom-clobbering}
@@ -1479,8 +1483,8 @@ application by naming elements through `id` or `name` attributes such that
 properties like `children` of an HTML element in the DOM are overshadowed by
 the malicious content.
 
-The Sanitizer API does not protect DOM clobbering attacks in its
-default state, but can be configured to remove `id` and `name` attributes.
+The Sanitizer API disallows the `id` and `name` attributes by default, but
+can be configured to allow them if desired.
 
 ## XSS with Script gadgets ## {#script-gadgets}
 
@@ -1512,13 +1516,13 @@ into a different parent element. An example for carrying out such an attack
 is by relying on the change of parsing behavior for foreign content or
 mis-nested tags.
 
-The Sanitizer API offers only functions that turn a string into a node tree.
-The context is supplied implicitly by all sanitizer functions:
+The Sanitizer API offers functions that combine parsing, sanitization and insertion.
+As such, the parsing context is supplied implicitly by all sanitizer functions:
 `Element.setHTML()` uses the current element; `Document.parseHTML()` creates a
 new document. Therefore Sanitizer API is not directly affected by mutated XSS.
 
 If a developer were to retrieve a sanitized node tree as a string, e.g. via
-`.innerHTML`, and to then parse it again then mutated XSS may occur.
+`.innerHTML`, to only parse or insert it again, a mutated XSS may still occur.
 We discourage this practice. If processing or passing of HTML as a
 string should be necessary after all, then any string should be considered
 untrusted and should be sanitized (again) when inserting it into the DOM. In
@@ -1527,6 +1531,483 @@ longer be considered as sanitized.
 
 A more complete treatment of mXSS can be found in [[MXSS]].
 
+
+# Index
+
+<em>This section is not normative.</em>
+
+## Elements and attributes not included in the default config ##  {#default-disallowed-elements}
+
+While the Sanitizer aims to disallow Cross-Site Scripting attacks, the default
+settings are a bit stricter and do not include elements that may change page
+settings, layout or fetch resources from other origins. The following elements
+can be allowed with a configuration, but the individual reasoning for disallowing
+them by default is given below.
+
+Some elements are disallowed for multiple reasons, the list below does NOT aim to be
+exhaustive. The following list will only mention the most concerning capability as the
+reason for not allowing an element by default. It does not list all of them.
+
+See also: [[#security-considerations]].
+
+: `<meta>`
+:: This element is not allowed, because it can set or modify global document state.
+
+: `<link>`
+:: This element is not allowed, because it can set or modify global document state.
+
+: `<a target>`
+:: The `target` attribute is not allowed, because it may lead to unintended consequences (e.g., targeting existing frames).
+
+: `<a download>`
+:: The `download` attribute is not allowed, because it could target content not intended for downloading.
+
+: `<a referrerpolicy>`
+:: The `referrerpolicy` attribute is not allowed, because it can override site-specific settings.
+
+: `<a rel>`
+:: The `rel` attribute is not allowed, because it can claim ownership or relationship of the whole document.
+
+: `<a ping>`
+:: The `ping` attribute is not allowed, because it could notify an unintended third-party of the link being clicked.
+
+
+: `<audio>`, `<canvas>`, `<embed>`, `<iframe>`, `<img>`, `<picture>`, `<video>`
+:: These elements for embedding content are not allowed, because it leads to HTTP requests to arbitrary hosts.
+
+: `<math>` MathML math
+:: The reasoning for the inclusion of MathML is solely based on [[SafeMathML]].
+
+: `<svg>`
+:: This element is not allowed, because it leads to HTTP requests to arbitrary hosts.
+
+: `<form>`, `<label>`, `<input>`, `<fieldset>`, `<legend>`, `<textarea>`, `<button>`, `<select>`, `<option>`, `<output>`
+:: These form elements are disallowed, we do not expect them in user-controlled content.
+
+: `<dialog>`, `<details>`
+:: These interactive elements are disallowed, we do not expect them in user-controlled content.
+
+
+## Elements that are **never** allowed ## {#never-allowed}
+
+  <table>
+   <caption>List of unsafe and disallowed elements</caption>
+   <thead>
+    <tr>
+     <th> Element
+     <th> Namespace
+     <th> Description
+   <tbody>
+
+    <tr>
+     <td><code>embed</code></td>
+     <td>http://www.w3.org/1999/xhtml</td>
+     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>frame</code></td>
+     <td>http://www.w3.org/1999/xhtml</td>
+     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>iframe</code></td>
+     <td>http://www.w3.org/1999/xhtml</td>
+     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>object</code></td>
+     <td>http://www.w3.org/1999/xhtml</td>
+     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>script</code></td>
+     <td>http://www.w3.org/1999/xhtml</td>
+     <td>This element is disallowed because it executes scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>script</code></td>
+     <td>http://www.w3.org/2000/svg</td>
+     <td>This element is disallowed because it executes scripts.</td>
+    </tr>
+
+    <tr>
+     <td><code>use</code></td>
+     <td>http://www.w3.org/2000/svg</td>
+     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+    </tr>
+  </table>
+
+
+## Event Handler Content Attributes
+
+All known event handler content attributes are disallowed, as they execute script.
+
+ <table>
+   <caption>List of all known and therefore disallowed event handler content attributes attributes</caption>
+   <thead>
+    <tr>
+     <th> Attribute
+   <tbody>
+ <tr>
+     <td><code>onafterprint</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onauxclick</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onbeforeinput</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onbeforematch</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onbeforeprint</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onbeforeunload</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onbeforetoggle</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onblur</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncancel</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncanplay</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncanplaythrough</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onchange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onclick</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onclose</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncontextlost</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncontextmenu</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncontextrestored</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncopy</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncuechange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oncut</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondblclick</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondrag</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondragend</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondragenter</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondragleave</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondragover</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondragstart</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondrop</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ondurationchange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onemptied</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onended</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onerror</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onfocus</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onformdata</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onhashchange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oninput</code></td>
+    </tr>
+
+    <tr>
+     <td><code>oninvalid</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onkeydown</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onkeypress</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onkeyup</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onlanguagechange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onload</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onloadeddata</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onloadedmetadata</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onloadstart</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmessage</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmessageerror</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmousedown</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmouseenter</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmouseleave</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmousemove</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmouseout</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmouseover</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onmouseup</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onoffline</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ononline</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpagehide</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpagereveal</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpageshow</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpageswap</code></td>
+    </tr>
+
+
+    <tr>
+     <td><code>onpaste</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpause</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onplay</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onplaying</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onpopstate</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onprogress</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onratechange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onreset</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onresize</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onrejectionhandled</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onscroll</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onscrollend</code></td>
+    </tr>
+
+
+    <tr>
+     <td><code>onsecuritypolicyviolation</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onseeked</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onseeking</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onselect</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onslotchange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onstalled</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onstorage</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onsubmit</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onsuspend</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ontimeupdate</code></td>
+    </tr>
+
+    <tr>
+     <td><code>ontoggle</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onunhandledrejection</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onunload</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onvolumechange</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onwaiting</code></td>
+    </tr>
+
+    <tr>
+     <td><code>onwheel</code></td>
+    </tr>
+  </table>
+
 # Acknowledgements # {#ack}
 
 This work is informed and inspired by [[DOMPURIFY]] from cure53,

From 7423640ca3d9fe1bf9066843a526f644ea49dff0 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Mon, 3 Nov 2025 13:30:51 +0100
Subject: [PATCH 2/7] review feedback - part 1

---
 index.bs | 519 +++++++++++++++----------------------------------------
 1 file changed, 137 insertions(+), 382 deletions(-)

diff --git a/index.bs b/index.bs
index 374add5..3639bda 100644
--- a/index.bs
+++ b/index.bs
@@ -54,6 +54,11 @@ text: report a warning to the console; type: dfn; url: https://console.spec.what
   "href": "https://www.bucksch.org/1/projects/mozilla/108153/",
   "title": "HTML Sanitizer",
   "publisher": "Ben Bucksch"
+  },
+  "XSS": {
+    "href": "https://developer.mozilla.org/de/docs/Web/Security/Attacks/XSS",
+    "title": "Cross-Site Scripting",
+    "publisher": "MDN Web Docs"
   }
 }
 </pre>
@@ -1452,17 +1457,18 @@ URLs, is as follows:
 
 # Security Considerations # {#security-considerations}
 
-The Sanitizer API is intended to prevent DOM-based Cross-Site Scripting
+The Sanitizer API is intended to prevent DOM-based Cross-Site Scripting [[XSS]]
 by traversing supplied HTML content and removing elements and attributes
 according to a configuration. The Sanitizer API ships a strict baseline,
 such that scripting can never be allowed (cf. [[#never-allowed]]).
 In addition to this, a default safe list includes further restrictions that may help
 prevent a wide range of undesirable effects. These include, elements that can override
 site-specific settings (e.g., `<meta>`), embed third-party content or change the
-layout of the page (e.g., `<img>`, `<style>`).
+layout of the page (e.g., `<img>`, `<style>`, `aria-` attributes).
 In addition, we disallow element and attribute configurations that lead to outgoing HTTP
 requests, and form controls. A detailed list is given in [[#default-disallowed-elements]].
 
+
 That being said, there are security issues which the correct usage of the
 Sanitizer API will not be able to protect against and the scenarios will be
 laid out in the following sections.
@@ -1522,7 +1528,7 @@ As such, the parsing context is supplied implicitly by all sanitizer functions:
 new document. Therefore Sanitizer API is not directly affected by mutated XSS.
 
 If a developer were to retrieve a sanitized node tree as a string, e.g. via
-`.innerHTML`, to only parse or insert it again, a mutated XSS may still occur.
+`.innerHTML`, to only parse or insert it again, mutated XSS may still occur.
 We discourage this practice. If processing or passing of HTML as a
 string should be necessary after all, then any string should be considered
 untrusted and should be sanitized (again) when inserting it into the DOM. In
@@ -1536,7 +1542,7 @@ A more complete treatment of mXSS can be found in [[MXSS]].
 
 <em>This section is not normative.</em>
 
-## Elements and attributes not included in the default config ##  {#default-disallowed-elements}
+## Elements and attributes not allowed in the default config ##  {#default-disallowed-elements}
 
 While the Sanitizer aims to disallow Cross-Site Scripting attacks, the default
 settings are a bit stricter and do not include elements that may change page
@@ -1550,43 +1556,153 @@ reason for not allowing an element by default. It does not list all of them.
 
 See also: [[#security-considerations]].
 
+### List of disallowed elements in the HTML namespace
+
 : `<meta>`
 :: This element is not allowed, because it can set or modify global document state.
 
 : `<link>`
 :: This element is not allowed, because it can set or modify global document state.
 
-: `<a target>`
+: The `<a>` element is allowed, but some attributes are disallowed by default. These are:
 :: The `target` attribute is not allowed, because it may lead to unintended consequences (e.g., targeting existing frames).
-
-: `<a download>`
 :: The `download` attribute is not allowed, because it could target content not intended for downloading.
-
-: `<a referrerpolicy>`
 :: The `referrerpolicy` attribute is not allowed, because it can override site-specific settings.
-
-: `<a rel>`
 :: The `rel` attribute is not allowed, because it can claim ownership or relationship of the whole document.
-
-: `<a ping>`
 :: The `ping` attribute is not allowed, because it could notify an unintended third-party of the link being clicked.
 
-
 : `<audio>`, `<canvas>`, `<embed>`, `<iframe>`, `<img>`, `<picture>`, `<video>`
 :: These elements for embedding content are not allowed, because it leads to HTTP requests to arbitrary hosts.
 
-: `<math>` MathML math
-:: The reasoning for the inclusion of MathML is solely based on [[SafeMathML]].
-
-: `<svg>`
-:: This element is not allowed, because it leads to HTTP requests to arbitrary hosts.
-
 : `<form>`, `<label>`, `<input>`, `<fieldset>`, `<legend>`, `<textarea>`, `<button>`, `<select>`, `<option>`, `<output>`
 :: These form elements are disallowed, we do not expect them in user-controlled content.
 
 : `<dialog>`, `<details>`
 :: These interactive elements are disallowed, we do not expect them in user-controlled content.
 
+: `<style>``
+:: This element is disallowed because it can change the layout of the page.
+
+### List of disallowed elements in the MathML namespace
+
+The `<math>` element and various additional elements are allowed.
+The list and their reasoning for the inclusion can be found in [[SafeMathML]].
+
+### List of disallowed elements in the SVG namespace
+
+FIXME: What about svg `<a>`. It doesn't appear in our list of allowed elements. Why?
+
+: `<animate>`
+:: This element is disallowed because SVG animations can modify and set attributes on other elements.
+
+: `<animateMotion>`
+:: This element is disallowed because we do not allow SVG animations (see above).
+
+: `<animateTransform>`
+:: This element is disallowed because we do not allow SVG animations (see above).
+
+: `<clipPath>´
+
+TODO FREDDY: Do we want to group all filter effect elements (fe...) in one entry?
+
+: `<feBlend>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feColorMatrix>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feComponentTransfer>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feComposite>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feConvolveMatrix>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feDiffuseLighting>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feDisplacementMap>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feDistantLight>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feDropShadow>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feFlood>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feFuncA>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feFuncB>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feFuncG>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feFuncR>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feGaussianBlur>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feImage>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feMerge>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feMergeNode>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feMorphology>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feOffset>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<fePointLight>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feSpecularLighting>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feSpotLight>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feTile>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<feTurbulence>`
+:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
+: `<filter>`
+:: :: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+
+
+: `<image>`
+:: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+
+: `<linearGradient>`
+:: This element is disallowed, because we do not allow SVG animations (see above).
+
+: `<mask>`
+:: This element is disallowed, because we do not allow WHY?
+
+: `<mpath>`
+:: This element is disallowed, because we do not allow SVG animations (see above).
+
+: `<pattern>`
+:: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+
+
+
+: `<radialGradient>`
+:: This element is disallowed, because we do not allow SVG animations (see above).
+
+: The `<svg>` element is allowed, but some attributes are disallowed by default. These are:
+:: The `src` attribute is not allowed because it leads to HTTP requests to arbitrary hosts.
+
+: `<set>`
+:: This element is disallowed, because we do not allow SVG animations (see above).
+
+: `<style>`
+:: This element is disallowed because it can change the layout of the page.
+
+: `<switch>`
+:: This element is disallowed because it can dynamically query and identify the user's settings.
+
+: `<symbol>`
+:: This element is disallowed because we do not allow the `<use>` element.
+
+: `<use>`
+:: This element is disallowed because it leads to HTTP requests to arbitrary hosts.
+
+: `<view>`
+:: This element is disallowed because it can allow selectively switching what is displayed
+
+TODO: Is svg:view actually a concern? From the surface, this looks like you can declare stuff to be switched, but not actually switch views. Maybe OK?
+
+
 
 ## Elements that are **never** allowed ## {#never-allowed}
 
@@ -1645,368 +1761,7 @@ See also: [[#security-considerations]].
 
 ## Event Handler Content Attributes
 
-All known event handler content attributes are disallowed, as they execute script.
-
- <table>
-   <caption>List of all known and therefore disallowed event handler content attributes attributes</caption>
-   <thead>
-    <tr>
-     <th> Attribute
-   <tbody>
- <tr>
-     <td><code>onafterprint</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onauxclick</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onbeforeinput</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onbeforematch</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onbeforeprint</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onbeforeunload</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onbeforetoggle</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onblur</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncancel</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncanplay</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncanplaythrough</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onchange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onclick</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onclose</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncontextlost</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncontextmenu</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncontextrestored</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncopy</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncuechange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oncut</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondblclick</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondrag</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondragend</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondragenter</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondragleave</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondragover</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondragstart</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondrop</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ondurationchange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onemptied</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onended</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onerror</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onfocus</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onformdata</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onhashchange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oninput</code></td>
-    </tr>
-
-    <tr>
-     <td><code>oninvalid</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onkeydown</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onkeypress</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onkeyup</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onlanguagechange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onload</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onloadeddata</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onloadedmetadata</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onloadstart</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmessage</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmessageerror</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmousedown</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmouseenter</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmouseleave</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmousemove</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmouseout</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmouseover</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onmouseup</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onoffline</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ononline</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpagehide</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpagereveal</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpageshow</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpageswap</code></td>
-    </tr>
-
-
-    <tr>
-     <td><code>onpaste</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpause</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onplay</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onplaying</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onpopstate</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onprogress</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onratechange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onreset</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onresize</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onrejectionhandled</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onscroll</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onscrollend</code></td>
-    </tr>
-
-
-    <tr>
-     <td><code>onsecuritypolicyviolation</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onseeked</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onseeking</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onselect</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onslotchange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onstalled</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onstorage</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onsubmit</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onsuspend</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ontimeupdate</code></td>
-    </tr>
-
-    <tr>
-     <td><code>ontoggle</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onunhandledrejection</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onunload</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onvolumechange</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onwaiting</code></td>
-    </tr>
-
-    <tr>
-     <td><code>onwheel</code></td>
-    </tr>
-  </table>
+All known [=event handler content attributes=] are disallowed, as they execute script.
 
 # Acknowledgements # {#ack}
 

From c7060199d023ce41b91fed604ba3670dfaafd7c4 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Mon, 3 Nov 2025 13:58:32 +0100
Subject: [PATCH 3/7] no comma before because#

---
 index.bs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/index.bs b/index.bs
index 3639bda..a81c5f4 100644
--- a/index.bs
+++ b/index.bs
@@ -1656,34 +1656,34 @@ TODO FREDDY: Do we want to group all filter effect elements (fe...) in one entry
 : `<feTurbulence>`
 :: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
 : `<filter>`
-:: :: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+:: :: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
 
 
 : `<image>`
-:: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+:: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
 
 : `<linearGradient>`
-:: This element is disallowed, because we do not allow SVG animations (see above).
+:: This element is disallowed because we do not allow SVG animations (see above).
 
 : `<mask>`
-:: This element is disallowed, because we do not allow WHY?
+:: This element is disallowed because we do not allow WHY?
 
 : `<mpath>`
-:: This element is disallowed, because we do not allow SVG animations (see above).
+:: This element is disallowed because we do not allow SVG animations (see above).
 
 : `<pattern>`
-:: This elements is not allowed, because it leads to HTTP requests to arbitrary hosts.
+:: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
 
 
 
 : `<radialGradient>`
-:: This element is disallowed, because we do not allow SVG animations (see above).
+:: This element is disallowed because we do not allow SVG animations (see above).
 
 : The `<svg>` element is allowed, but some attributes are disallowed by default. These are:
 :: The `src` attribute is not allowed because it leads to HTTP requests to arbitrary hosts.
 
 : `<set>`
-:: This element is disallowed, because we do not allow SVG animations (see above).
+:: This element is disallowed because we do not allow SVG animations (see above).
 
 : `<style>`
 :: This element is disallowed because it can change the layout of the page.

From e518c72d5e344e600aa54d8b246054f7722876f7 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Wed, 5 Nov 2025 08:54:02 +0100
Subject: [PATCH 4/7] rewrite to ensure we include ideally all elements - part
 1

---
 index.bs | 44 +++++++++++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/index.bs b/index.bs
index a81c5f4..aea7198 100644
--- a/index.bs
+++ b/index.bs
@@ -1558,31 +1558,49 @@ See also: [[#security-considerations]].
 
 ### List of disallowed elements in the HTML namespace
 
-: `<meta>`
-:: This element is not allowed, because it can set or modify global document state.
+
+: The `<a>` element is allowed, but some attributes are disallowed by default. These are:
+:: The `target` attribute is not allowed because it may lead to unintended consequences (e.g., targeting existing frames).
+:: The `download` attribute is not allowed because it could target content not intended for downloading.
+:: The `referrerpolicy` attribute is not allowed because it can override site-specific settings.
+:: The `rel` attribute is not allowed because it can claim ownership or relationship of the whole document.
+:: The `ping` attribute is not allowed because it could notify an unintended third-party of the link being clicked.
+
+: `<area>`
+:: This element is not allowed because it requires a `<map>`, which is also not allowed.
+: `<base>`
+:: This element is not supported because it overrides the default base URL for all links in the document.
+
 
 : `<link>`
-:: This element is not allowed, because it can set or modify global document state.
+:: This element is not allowed because it can set or modify global document state.
 
-: The `<a>` element is allowed, but some attributes are disallowed by default. These are:
-:: The `target` attribute is not allowed, because it may lead to unintended consequences (e.g., targeting existing frames).
-:: The `download` attribute is not allowed, because it could target content not intended for downloading.
-:: The `referrerpolicy` attribute is not allowed, because it can override site-specific settings.
-:: The `rel` attribute is not allowed, because it can claim ownership or relationship of the whole document.
-:: The `ping` attribute is not allowed, because it could notify an unintended third-party of the link being clicked.
+: `<map>`
+:: This element is not allowed because images are not allowed by default.
 
-: `<audio>`, `<canvas>`, `<embed>`, `<iframe>`, `<img>`, `<picture>`, `<video>`
-:: These elements for embedding content are not allowed, because it leads to HTTP requests to arbitrary hosts.
+: `<meta>`
+:: This element is not allowed because it can set or modify global document state.
+
+: `<noscript>`
+:: This element is not allowed because it
+
+: `<audio>`, `<canvas>`, `<embed>`, `<iframe>`, `<img>`, `<object>`, `<picture>`, `<source>, `<track>` `<video>`
+:: These elements for embedding content are not allowed because it leads to HTTP requests to arbitrary hosts.
 
-: `<form>`, `<label>`, `<input>`, `<fieldset>`, `<legend>`, `<textarea>`, `<button>`, `<select>`, `<option>`, `<output>`
+: `<datalist>`, `<form>`, `<label>`, `<input>`, `<fieldset>`, `<legend>`, `<textarea>`, `<button>`, `<select>`, `<option>`,  `<optgroup>`, `<output>`, `<progress>`, `<select>`, <selectedcontent>
 :: These form elements are disallowed, we do not expect them in user-controlled content.
 
-: `<dialog>`, `<details>`
+: `<dialog>`, `<details>`, `<summary>`
 :: These interactive elements are disallowed, we do not expect them in user-controlled content.
 
 : `<style>``
 :: This element is disallowed because it can change the layout of the page.
 
+: `<template>`, `<slot>`,
+
+TODO Freddy: Also add non-conforming when they are not supported? These would be https://html.spec.whatwg.org/#non-conforming-features
+
+
 ### List of disallowed elements in the MathML namespace
 
 The `<math>` element and various additional elements are allowed.

From d65965d6f0be64a41f3a9ae975160fd3a4b5ee7a Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Wed, 5 Nov 2025 08:58:10 +0100
Subject: [PATCH 5/7] reduce PR to defer tables of allowed/disallowed elements
 for a follow-up

---
 index.bs | 171 +------------------------------------------------------
 1 file changed, 1 insertion(+), 170 deletions(-)

diff --git a/index.bs b/index.bs
index aea7198..ad7150b 100644
--- a/index.bs
+++ b/index.bs
@@ -1544,183 +1544,14 @@ A more complete treatment of mXSS can be found in [[MXSS]].
 
 ## Elements and attributes not allowed in the default config ##  {#default-disallowed-elements}
 
-While the Sanitizer aims to disallow Cross-Site Scripting attacks, the default
+While the Sanitizer aims to disallow Cross-Site Scripting attacks [[XSS]], the default
 settings are a bit stricter and do not include elements that may change page
 settings, layout or fetch resources from other origins. The following elements
 can be allowed with a configuration, but the individual reasoning for disallowing
 them by default is given below.
 
-Some elements are disallowed for multiple reasons, the list below does NOT aim to be
-exhaustive. The following list will only mention the most concerning capability as the
-reason for not allowing an element by default. It does not list all of them.
-
 See also: [[#security-considerations]].
 
-### List of disallowed elements in the HTML namespace
-
-
-: The `<a>` element is allowed, but some attributes are disallowed by default. These are:
-:: The `target` attribute is not allowed because it may lead to unintended consequences (e.g., targeting existing frames).
-:: The `download` attribute is not allowed because it could target content not intended for downloading.
-:: The `referrerpolicy` attribute is not allowed because it can override site-specific settings.
-:: The `rel` attribute is not allowed because it can claim ownership or relationship of the whole document.
-:: The `ping` attribute is not allowed because it could notify an unintended third-party of the link being clicked.
-
-: `<area>`
-:: This element is not allowed because it requires a `<map>`, which is also not allowed.
-: `<base>`
-:: This element is not supported because it overrides the default base URL for all links in the document.
-
-
-: `<link>`
-:: This element is not allowed because it can set or modify global document state.
-
-: `<map>`
-:: This element is not allowed because images are not allowed by default.
-
-: `<meta>`
-:: This element is not allowed because it can set or modify global document state.
-
-: `<noscript>`
-:: This element is not allowed because it
-
-: `<audio>`, `<canvas>`, `<embed>`, `<iframe>`, `<img>`, `<object>`, `<picture>`, `<source>, `<track>` `<video>`
-:: These elements for embedding content are not allowed because it leads to HTTP requests to arbitrary hosts.
-
-: `<datalist>`, `<form>`, `<label>`, `<input>`, `<fieldset>`, `<legend>`, `<textarea>`, `<button>`, `<select>`, `<option>`,  `<optgroup>`, `<output>`, `<progress>`, `<select>`, <selectedcontent>
-:: These form elements are disallowed, we do not expect them in user-controlled content.
-
-: `<dialog>`, `<details>`, `<summary>`
-:: These interactive elements are disallowed, we do not expect them in user-controlled content.
-
-: `<style>``
-:: This element is disallowed because it can change the layout of the page.
-
-: `<template>`, `<slot>`,
-
-TODO Freddy: Also add non-conforming when they are not supported? These would be https://html.spec.whatwg.org/#non-conforming-features
-
-
-### List of disallowed elements in the MathML namespace
-
-The `<math>` element and various additional elements are allowed.
-The list and their reasoning for the inclusion can be found in [[SafeMathML]].
-
-### List of disallowed elements in the SVG namespace
-
-FIXME: What about svg `<a>`. It doesn't appear in our list of allowed elements. Why?
-
-: `<animate>`
-:: This element is disallowed because SVG animations can modify and set attributes on other elements.
-
-: `<animateMotion>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: `<animateTransform>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: `<clipPath>´
-
-TODO FREDDY: Do we want to group all filter effect elements (fe...) in one entry?
-
-: `<feBlend>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feColorMatrix>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feComponentTransfer>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feComposite>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feConvolveMatrix>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feDiffuseLighting>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feDisplacementMap>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feDistantLight>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feDropShadow>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feFlood>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feFuncA>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feFuncB>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feFuncG>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feFuncR>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feGaussianBlur>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feImage>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feMerge>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feMergeNode>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feMorphology>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feOffset>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<fePointLight>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feSpecularLighting>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feSpotLight>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feTile>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<feTurbulence>`
-:: This element is disallowed because we do not allow SVG filters (see `<filter>` below).
-: `<filter>`
-:: :: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
-
-
-: `<image>`
-:: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
-
-: `<linearGradient>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: `<mask>`
-:: This element is disallowed because we do not allow WHY?
-
-: `<mpath>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: `<pattern>`
-:: This elements is not allowed because it leads to HTTP requests to arbitrary hosts.
-
-
-
-: `<radialGradient>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: The `<svg>` element is allowed, but some attributes are disallowed by default. These are:
-:: The `src` attribute is not allowed because it leads to HTTP requests to arbitrary hosts.
-
-: `<set>`
-:: This element is disallowed because we do not allow SVG animations (see above).
-
-: `<style>`
-:: This element is disallowed because it can change the layout of the page.
-
-: `<switch>`
-:: This element is disallowed because it can dynamically query and identify the user's settings.
-
-: `<symbol>`
-:: This element is disallowed because we do not allow the `<use>` element.
-
-: `<use>`
-:: This element is disallowed because it leads to HTTP requests to arbitrary hosts.
-
-: `<view>`
-:: This element is disallowed because it can allow selectively switching what is displayed
-
-TODO: Is svg:view actually a concern? From the surface, this looks like you can declare stuff to be switched, but not actually switch views. Maybe OK?
-
-
 
 ## Elements that are **never** allowed ## {#never-allowed}
 

From 0f24e3310df94aa8d2a7bdf16428338636983706 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Wed, 5 Nov 2025 09:55:14 +0100
Subject: [PATCH 6/7] showcase how we could reason about html/svg/mathml
 elements/attributes in a cohesive way with a table and footnotes.

---
 index.bs | 410 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 404 insertions(+), 6 deletions(-)

diff --git a/index.bs b/index.bs
index ad7150b..fc1d16e 100644
--- a/index.bs
+++ b/index.bs
@@ -1542,6 +1542,394 @@ A more complete treatment of mXSS can be found in [[MXSS]].
 
 <em>This section is not normative.</em>
 
+### Elements and attributes in the MathML namespace
+
+The `<math>` element and various additional elements are allowed.
+The list and their reasoning for the inclusion can be found in [[SafeMathML]].
+
+### Elements and attributes in the SVG namespace
+
+Features are either allowed, allowable (e.g., disallowed by default but can be included in a custom configuration) or completely disallowed.
+
+<table>
+   <caption>Global Attributes in the SVG Namespace</caption>
+   <thead>
+    <tr>
+     <th> Attribute
+     <th> Decision
+     <th> Reasoning (if disallowed)
+   <tbody>
+
+    <tr>
+     <td><code>cx</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>cy</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>height</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>width</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>x</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>y</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>d</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-1"><sup>1</sup></a></td>
+    </tr>
+
+    <tr>
+     <td><code>fill</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>transform</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>alignment-base</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>baseline-shift</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>clip-path</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>clip-rule</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>color</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+    <tr>
+     <td><code>color-interpolation</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>color-interpolation-filters</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-3"><sup>3</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>cursor</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>direction</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>display</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>dominant-baseline</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>fill-opacity</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>fill-rule</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>filter</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-2"><sup>2</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>flood-color</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-2"><sup>2</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>flood-opacity</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-2"><sup>2</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>font-family</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-size</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-size-adjust</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-stretch</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-style</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-variant</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>font-weight</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>glyph-orientation-horizontal</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-3"><sup>3</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>glyph-orientation-vertical</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-3"><sup>3</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>image-rendering</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-4"><sup>4</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>letter-spacing</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>lighting-color</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-3"><sup>3</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>marker-end</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>marker-mid</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>marker-start</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>mask</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-5"><sup>5</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>mask-type</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-5"><sup>5</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>opacity</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>overflow</code></td>
+     <td>Allowable</td>
+     <td><a href="#svg-attr-6"><sup>6</sup></a></td>
+    </tr>
+    <tr>
+     <td><code>paint-order</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>pointer-events</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>shape-rendering</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stop-color</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stop-opacity</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-dasharray</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-dashoffset</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-linecap</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-linejoin</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-miterlimit</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-opacity</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>stroke-width</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>text-anchor</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>text-decoration</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>text-overflow</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>text-rendering</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>transform-origin</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>unicode-bidi</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>vector-effect</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>visibility</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>white-space</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>word-spacing</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+    <tr>
+     <td><code>writing-mode</code></td>
+     <td>Allowed</td>
+     <td></td>
+    </tr>
+
+
+</tbody>
+</table>
+
+### Legend of exclusion criteria for SVG features.
+<ol>
+<li id="svg-attr-1">This attribute is disallowed as a global attribute, we only want to allow it on some elements.
+<li id="svg-attr-2">This attribute is disallowed because we do not allow the SVG `<filter>` element.
+<li id="svg-attr-3">This attribute is disallowed because it is deprecated
+<li id="svg-attr-4">This attribute is disallowed because we do not allow the `<image>` element.
+<li id="svg-attr-5">This attribute is disallowed because we do not allow the `<mask>` element.
+<li id="svg-attr-6">This attribute is disallowed because we do not allow the the element to impact the page layout.
+</ol>
+
+
 ## Elements and attributes not allowed in the default config ##  {#default-disallowed-elements}
 
 While the Sanitizer aims to disallow Cross-Site Scripting attacks [[XSS]], the default
@@ -1555,6 +1943,8 @@ See also: [[#security-considerations]].
 
 ## Elements that are **never** allowed ## {#never-allowed}
 
+TODO: Freddy will fold this into the individual HTML and SVG lists. To be written above.
+
   <table>
    <caption>List of unsafe and disallowed elements</caption>
    <thead>
@@ -1567,19 +1957,19 @@ See also: [[#security-considerations]].
     <tr>
      <td><code>embed</code></td>
      <td>http://www.w3.org/1999/xhtml</td>
-     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+     <td><a href="#html-el-1"><sup>1</sup></a></td>
     </tr>
 
     <tr>
      <td><code>frame</code></td>
      <td>http://www.w3.org/1999/xhtml</td>
-     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+     <td><a href="#html-el-1"><sup>1</sup></a></td>
     </tr>
 
     <tr>
      <td><code>iframe</code></td>
      <td>http://www.w3.org/1999/xhtml</td>
-     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+     <td><a href="#html-el-1"><sup>1</sup></a></td>
     </tr>
 
     <tr>
@@ -1591,22 +1981,30 @@ See also: [[#security-considerations]].
     <tr>
      <td><code>script</code></td>
      <td>http://www.w3.org/1999/xhtml</td>
-     <td>This element is disallowed because it executes scripts.</td>
+     <td><a href="#html-el-2"><sup>2</sup></a></td>
     </tr>
 
     <tr>
      <td><code>script</code></td>
      <td>http://www.w3.org/2000/svg</td>
-     <td>This element is disallowed because it executes scripts.</td>
+     <td><a href="#html-el-2"><sup>2</sup></a></td>
     </tr>
 
     <tr>
      <td><code>use</code></td>
      <td>http://www.w3.org/2000/svg</td>
-     <td>This element is disallowed because it can include other, untrusted documents and including scripts.</td>
+     <td><a href="#html-el-1"><sup>1</sup></a></td>
     </tr>
   </table>
 
+### Legend of exclusion criteria for HTML features.
+<ol>
+<li id="html-el-1">This element is always disallowed because it can include other, untrusted documents and including scripts.
+<li id="html-el-2">This element is always disallowed because it executes scripts.
+</ol>
+
+
+
 
 ## Event Handler Content Attributes
 

From 1287ee6a4a0fa730b1a14f43b69fe0d910ebae3c Mon Sep 17 00:00:00 2001
From: Frederik Braun <fbraun@mozilla.com>
Date: Thu, 6 Nov 2025 11:04:54 +0100
Subject: [PATCH 7/7] clarify ARIA

---
 index.bs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/index.bs b/index.bs
index fc1d16e..c1354cc 100644
--- a/index.bs
+++ b/index.bs
@@ -1463,8 +1463,8 @@ according to a configuration. The Sanitizer API ships a strict baseline,
 such that scripting can never be allowed (cf. [[#never-allowed]]).
 In addition to this, a default safe list includes further restrictions that may help
 prevent a wide range of undesirable effects. These include, elements that can override
-site-specific settings (e.g., `<meta>`), embed third-party content or change the
-layout of the page (e.g., `<img>`, `<style>`, `aria-` attributes).
+site-specific settings (e.g., `<meta>`), embed third-party content, or change the
+layout/semantics of the page (e.g., `<img>`, `<style>`, `aria-` attributes).
 In addition, we disallow element and attribute configurations that lead to outgoing HTTP
 requests, and form controls. A detailed list is given in [[#default-disallowed-elements]].