[arcwrightstudio]

Drawing between pixels is on by default and scrolling boxes glide by default (see CHANGELOG.md), with a measured comparison in the README.

• Svifa chooses the blocks that scroll with the content and gives each a layer of its own, split around fixed elements and z-indexes that reach past a block. Where a layer would change what is drawn over what, it draws on whole pixels and says why once in the console. data-svifa-subpixel="off" and subpixel: false turn it off.
• Scrolling boxes inside the scroller glide with the same feel and hand the wheel on at their end. nested: 'native' leaves them to the browser and a function decides for each box. While the page glides, a box's content moves with it exactly.
• Zoomed to a part of a pixel (a browser zoom such as 80% or a screen scale such as 125%), the page and its boxes are drawn from where the browser draws the scroll position, so a glide no longer shimmers. The position Svifa reports is unchanged. Tests cover a device scale of 0.8, 0.9, 1.25 and 1.5 in every engine and the browser's own zoom at 80% and 125% in Chromium.
• At such a scale, before the browser shows which places it keeps, a glide is never reported past where it was sent, and a glide on whole pixels never takes its last pixel early.
• Drawn on whole pixels, a glide keeps an even pace to its end.
• A glide drawn between pixels never runs past the end of the page, and in Firefox the wheel over a textarea stays with the textarea.
• The README compares Svifa with the most used smooth scroll libraries, measured on the same page in Chrome, Edge, Firefox and WebKit.
• Tests for something only some engines have are tagged and run only there; none is reported skipped. The property tests also run at a device scale of 1.25.