Donner targets SVG 2 conformance. The following SVG 1.1 features are deprecated or removed in SVG 2 and are intentionally not implemented.

Filter Inputs: BackgroundImage and BackgroundAlpha

SVG 1.1 behavior: The enable-background attribute on a container element captured a snapshot of the canvas behind it. Filter primitives could reference this snapshot via in="BackgroundImage" or in="BackgroundAlpha".

SVG 2 status: Removed. The SVG 2 spec no longer defines enable-background, BackgroundImage, or BackgroundAlpha.

Donner behavior: These input names are parsed as unresolved named references, producing transparent black (the SVG spec behavior for unresolved filter inputs). No warning is emitted.

Modern alternative: CSS compositing via mix-blend-mode and isolation properties provides equivalent functionality for blending with backdrop content.

Affected resvg tests: a-enable-background-* (category disabled), e-filter-032 (skipped), e-filter-033 (skipped).

SVG Fonts (<font>, <glyph>, <missing-glyph>, etc.)

SVG 1.1 behavior: Defined an inline font format using SVG path data for glyph outlines.

SVG 2 status: Removed entirely. WOFF/WOFF2 and system fonts are the standard mechanisms.

Donner behavior: These elements are not recognized. Donner supports TrueType/OpenType fonts via stb_truetype, WOFF2 via Brotli decompression, and optionally HarfBuzz for complex text shaping.

<cursor> Element

SVG 1.1 behavior: Defined a custom cursor image inline in SVG.

SVG 2 status: Removed. CSS cursor property is the standard mechanism.

Donner behavior: Not implemented.

<altGlyph>, <altGlyphDef>, <altGlyphItem>, <glyphRef>

SVG 1.1 behavior: Allowed substituting alternate glyph representations.

SVG 2 status: Removed. OpenType font features (accessed via font-feature-settings) provide this functionality.

Donner behavior: Not implemented.

<tref> Element

SVG 1.1 behavior: Referenced text content from another element by ID.

SVG 2 status: Removed.

Donner behavior: Not implemented.

The Clip Property (CSS 2 Clip Rect)

SVG 1.1 behavior: clip: rect(top, right, bottom, left) on <svg>, <symbol>, <image>, <foreignObject>, <pattern>.

SVG 2 status: Deprecated in favor of clip-path.

Donner behavior: Not implemented. Use clip-path with clipPathUnits="userSpaceOnUse" and an inset() shape instead.

xml:base, xml:lang, xml:space

SVG 2 status: xml:base removed. xml:lang replaced by lang. xml:space replaced by CSS white-space.

Donner behavior: xml:space is parsed for <text> whitespace handling. xml:base and xml:lang are not implemented.