Pan is a variable type system. The idea is to slice the glyphs in various ways and draw contours with the slice-data.
Since the drawings are not compatible, featureSubstitutions are needed. Currently five axes [Steps, Angle, Shape, Offset, Inner] controle what glyph is shown. A special set of tools was needed to create the GSUB table that can handle this.
I recommend to view my site in Chrome or Firefox, since it handles Variable Fonts much better than MacOS’ Core Text.
I started creating this font system in 2017. Back then, in MacOS, only one axis was working for featureSubstitutions. Now in 2020, it seems that it is still not fully solved in MacOS.
Here is a visualisation of my workflow.