I’ve eliminated STYLE_DEBUG because it wasn’t a full implementation. More or less, $concatenate_scripts was a bottleneck as it controls both CSS and JS. You now only need SCRIPT_DEBUG to use the unconcatenated development scripts and styles. https://core.trac.wordpress.org/ticket/12237

WP_DEBUG is now defined in wp-config-sample.php, with a note: “It is strongly recommended that plugin and theme developers use WP_DEBUG in their development environments.” Ideally, this will raise awareness and usage of WP_DEBUG among developers. https://core.trac.wordpress.org/ticket/12236

Not nearly as important, but there’s also some new inline documentation on the various debug constants, after some confusion about the purpose of WP_DEBUG_DISPLAY: https://core.trac.wordpress.org/changeset/13176