Presets are named collections of settings that determine basically everything about JPT's output. Think of them like frameworks that you can plug images into; the preset determines what markup, what image sizes, and what image formats to create, while the picture tag determines which image(s) will be used. They are stored in
_data/picture.yml. You will have to create this file, and probably the
_data/ directory as well.
Any settings which are specific to particular markup formats are documented on their respective markup format page.
# _data/picture.yml presets: (name): (option): (setting) (option): (setting) (...) (...)
# _data/picture.yml presets: default: formats: [webp, original] widths: [200, 400, 800, 1600] link_source: true lazy: markup: data_auto widths: [200, 400, 800, 1600] link_source: true noscript: true
Media queries are not presets, but they are used when writing them. They are defined in
_data/picture.yml alongside presets. They look like this:
# _data/picture.yml media_queries: (name): '(media query)' (name): '(media query)' (name): '(media query)'
media_queries: full_width: 'min-width: 901px' tablet: 'min-width: 601px' mobile: 'max-width: 600px'
More information here.