.ai import: a Drop Shadow with Darkness comes in with its Darkness

An object whose art style had a Drop Shadow with Darkness (a csrc
other than 0 in the shadow filter's dictionary) came in as its drawn
look, with a warning that its appearance isn't editable yet. With a
Color shadow instead, the same object comes in as itself with its
fill, stroke and shadow.

The reader now reads such a shadow as Drop Shadow with shade
"darkness" and darkness set to the filter's dark value, a percentage
kept within 0 to 100, or 100 when the value is missing or not a
finite number. The shadow's other keys are read as for a shadow with Color,
and the object comes in as itself wherever it would with a shadow with
Color. A shadow with Color comes in with the same params as before.
The import fuzz's .ai tokens now include csrc and dark.

Docs: docs/target-app-parity.md.

docs/target-app-parity.md

@@ -683,7 +683,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 
 - **Raster effects after document and view changes:** a cached drop shadow, outer glow or filtered content is made again when something its content reads from outside the object changes: a pattern's art or tiling, a symbol shown inside another symbol, a brush definition, an image's pixels, the raster resolution (De-Interlace), Page Knockout Group, Document Setup's substitution highlights, a layer's Dim Images, the color settings, the fonts, Pixel Preview, Anti-aliased Artwork, Overprint Preview and isolation mode. A thumbnail under Color Halftone or Mezzotint is made again when the document's color mode changes. Raster effects (blur, shadow, glow, grain) drawn after a pattern, radial or freeform gradient fill export at their place and size (#1541, fixes #1536).
 
-- **Drop Shadow's Darkness:** Effect › Stylize › Drop Shadow… has Color and Darkness as radio buttons, each with its field, and the Appearance panel's inline editor has the two radio buttons in its Shade row (`shade`: `color` or `darkness`; `darkness`: 0 to 100%, 100 by default). Color is the default, and a shadow saved without these keys draws as before. With Darkness the shadow is the object's own colors with black added: in a CMYK document their cyan, magenta and yellow stay and their black K becomes K + darkness × (1 − K), and in an RGB document each channel is multiplied by 1 − darkness. Darkness 0% gives the object's color; 100% gives black in an RGB document and keeps the colors under 100% black in a CMYK one. SVG export writes the object blurred, moved and darkened with `feComponentTransfer` (screen colors, in a CMYK document too), and SVG import reads it back; CSS export leaves the shadow out and marks the object unsupported. Behavior reference: Illustrator CC Help (2014, [PDF](https://help.adobe.com/archive/en/illustrator/cc/2014/illustrator_reference.pdf)), page 428 (PDF page 434).
+- **Drop Shadow's Darkness:** Effect › Stylize › Drop Shadow… has Color and Darkness as radio buttons, each with its field, and the Appearance panel's inline editor has the two radio buttons in its Shade row (`shade`: `color` or `darkness`; `darkness`: 0 to 100%, 100 by default). Color is the default, and a shadow saved without these keys draws as before. With Darkness the shadow is the object's own colors with black added: in a CMYK document their cyan, magenta and yellow stay and their black K becomes K + darkness × (1 − K), and in an RGB document each channel is multiplied by 1 − darkness. Darkness 0% gives the object's color; 100% gives black in an RGB document and keeps the colors under 100% black in a CMYK one. SVG export writes the object blurred, moved and darkened with `feComponentTransfer` (screen colors, in a CMYK document too), and SVG import reads it back; CSS export leaves the shadow out and marks the object unsupported. When a `.ai`, EPS or PDF opens from its editing data, a Drop Shadow with Darkness in an object's art style is read as one with Color is, with the shadow's Darkness percentage (100% when the style gives none). Behavior reference: Illustrator CC Help (2014, [PDF](https://help.adobe.com/archive/en/illustrator/cc/2014/illustrator_reference.pdf)), page 428 (PDF page 434).
 
 - **Live objects after document changes:** a blend, envelope or repeat, with or without an effect of its own, is evaluated again when one of these changes: the tiling of a pattern whose tiles an envelope bends (Distort Pattern Fills), a symbol shown inside a symbol, a pattern or an opacity mask, the fonts of its type, a placed document's file once the file is read, and the color settings. A gradient mesh, with or without an effect of its own, is colored again when the color settings change.