Clicking an Opacity row in the Appearance panel (a fill's or stroke's, or
the object's) opens a popup with the same blend-mode dropdown, opacity
field and slider as the Transparency panel (widgets::opacity_blend), and
edits that item through transparency.set. The blend-mode dropdown draws a
separator between the BlendMode::group() groups, also for the blend-mode
parameters of effect dialogs and inline effect editors. Fills and strokes
of type objects composite with their own opacity and blend mode.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>