Version 2 of the avar (Axis Variations) table enables font designers to create variable fonts with better control over interpolation. While the original variable font spec handles axes independently, avar2 allows axes to influence one another. This leads to fonts that are easier to use for content authors to use, and enable compact storage. Support for this feature in Blink means, activating a compile flag in HarfBuzz that processes the version 2 additional fields of the avar table to extend axis variations processing. Avar2 works by using the same familiar concepts of font variations, but applying the variable delta values to the design axis specifications itself. Plus, it allows doing this over a range of multiple axes. As an example, it allows the creation of "meta sliders" which control multiple variation axes at once, alleviating the user from fine-tuning and finding a useful corner of the font's design space. Avar2 gives font designers better control over the usable variation space of their font, and allows coordinating the adjustment of design axes across several axes. By defining the relationships between axes mathematically within the avar version 2 table, fonts can achieve complex designs with fewer masters, leading to smaller file sizes, because the interpolation is stored more efficiently.
Provide interoperability for this new feature of the of the Open Font Format font standard.
Explainers: https://github.com/harfbuzz/boring-expansion-spec/blob/main/avar2.md