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.

Legacy Glyph Orientation Properties

SVG 1.1 behavior: glyph-orientation-horizontal and glyph-orientation-vertical selected per-glyph rotation in horizontal and vertical text.

SVG 2 status: glyph-orientation-horizontal was removed. glyph-orientation-vertical was obsoleted and replaced by text-orientation; SVG 2 retains only a narrow compatibility alias for auto, 0, and 90 values.

Donner behavior: The legacy property names are recognized but do not have independent layout behavior. The narrow glyph-orientation-vertical compatibility alias is not yet applied. Modern vertical text should use writing-mode: vertical-rl or vertical-lr together with text-orientation.

Obsolete SVG 1.1 Writing-Mode Values

SVG 1.1 behavior: Values such as lr, lr-tb, rl, rl-tb, tb, tb-rl, and tb-lr selected horizontal or vertical text flow.

SVG 2 status: The distinct values are obsolete. CSS Writing Modes maps them to horizontal-tb, vertical-rl, or vertical-lr for compatibility.

Donner behavior: The parser immediately maps the obsolete spellings to their modern computed values. There is no separate legacy layout path.

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 Language and Whitespace Attributes

SVG 2 status: xml:base was removed. xml:lang remains a current XML language attribute, and SVG 2 also defines lang. xml:space was replaced by CSS white-space.

Donner behavior: xml:space is parsed for <text> whitespace handling. xml:base and xml:lang are not implemented. The implemented systemLanguage conditional-processing attribute is a separate feature and does not supply text language or font selection.