Why do WordPress adds the id=”handle-{js|css}” attribute to scripts and stylesheet?
The id attribute was added to the <style> tags in WordPress v4.1 (2014) — see the Trac changesets 29956 and 29958 which both mentioned ticket #30032 (“Add ID attribute to style element from wp_add_inline_style()“): In order to support partial preview refreshes (#27355), it is important for all partials being updated to have an element with …