FF139 SVG discard element and api removed - expr feature too

[hamishwillee]

FF139 (uplifted from FF140) removes experimental support for the SVG <discard> element added behind pref in FF136, and the SVGDiscardElement interface added to release in FF136.
I've removed the experimental feature entirely as it never released.

I've removed the <discard> element with direct as discussed in #26883 and all links.

The SVGDiscardElement is reverted to experimental, but may be being deleted too (depends on BCD). This can merge and I'll do that later if needed.

Associated docs work can be tracked in #39618

[github-actions]

Preview URLs (6 pages)

• /en-US/docs/Mozilla/Firefox/Experimental_features
• /en-US/docs/Web/API/SVGDiscardElement
• /en-US/docs/Web/SVG/Reference/Attribute/begin
• /en-US/docs/Web/SVG/Reference/Attribute/href
• /en-US/docs/Web/SVG/Reference/Element/animateTransform
• /en-US/docs/Web/SVG/Reference/Element

Flaws (3)

Note! 3 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Mozilla/Firefox/Experimental_features
Title: Experimental features in Firefox
Flaw count: 1

• broken_links:
  • Can't resolve /en-US/docs/Web/API/HTML_Sanitizer_API

---

URL: /en-US/docs/Web/SVG/Reference/Attribute/href
Title: href
Flaw count: 1

• macros:
  • Can't resolve /en-US/docs/Glossary/SMIL

---

URL: /en-US/docs/Web/SVG/Reference/Element/animateTransform
Title: <animateTransform>
Flaw count: 1

• macros:
  • Macro produces link /en-US/docs/Web/SVG/Element which is a redirect

External URLs (4)

URL: /en-US/docs/Web/SVG/Reference/Attribute/begin
Title: begin

• https://www.iso.org/iso-8601-date-and-time-format.html (1 time)
• https://www.w3.org/TR/smil-animation/ (1 time)

---

URL: /en-US/docs/Web/SVG/Reference/Attribute/href
Title: href

• https://www.w3.org/TR/smil-animation/ (1 time)

---

URL: /en-US/docs/Web/SVG/Reference/Element
Title: SVG element reference

• https://www.w3.org/TR/SVG2/struct.html (2 times)

(comment last updated: 2025-05-26 00:19:19)

[bsmth]

Thanks!