A PDF-compatible .ai paints the editor's page (an opaque white rectangle the
size of the page) before its first optional-content layer and outside every
layer. It came in as art: an extra "Page 1" layer with a page-sized white path
behind the artwork, which hid white art and gave SVG/PNG/PDF exports an
opaque background.
For pages with the editor's private data (the way the importer already tells
a .ai from a PDF), the first art outside every layer, painted before any
layer, is dropped when it is a plain fill-only rectangle in an opaque,
non-spot white, with normal blending, equal to the crop box (0.5 pt
tolerance). Plain PDFs keep such a rectangle as art (as the reference app
does when opening a PDF), and so does anything else: grey, smaller or larger
rectangles, strokes, translucency, white inks, fills over the layers.
The white-cover test the soft-mask reader used is now a shared helper.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
a18e671817