Reverting creates a new commit that undoes earlier changes, useful for backing out a single change or several related commits without rewriting history.

Flex items can overflow small screens because min-width:auto prevents shrinking below content size; min-width: 0 lets them fit available space.

Using self-hosted or purchased fonts with Webpack or Webpacker requires either bundling them from assets or packaging them locally for clean imports.

valid? no longer changes a record's state in rails_state_machine 1.1.2, preventing validation checks from causing unintended transitions.

Parallel test runs can exceed Redis’s default 16 databases on multi-core machines, causing ERR DB index is out of range; increasing the database limit resolves it.

Rails session hashes can ignore merge!, leaving new values invisible or unsaved. update loads the session for writing and avoids the mismatch.

Make Rome datepicker match Bootstrap 4 with utility classes and custom styling, while preserving Rome’s positioning CSS and internal state handling.

Webpacker 4 and Babel 7 change config files, package names, asset paths, and polyfill imports when upgrading a Rails app from Webpack 3.

Rails merges query string, request body, and routing data in params; request.query_parameters and request.path_parameters separate URL values from route data.

A float-clearing Sass mixin can avoid extra markup while preserving margin collapse and visible overflow. display: block is a safer clearfix choice than display: table or overflow: hidden.

Flash-free copy-to-clipboard handling with clipboard.js, including success and error callbacks, text selection feedback, and support for text fields or data attributes.

Moving away from jQuery improves performance, reduces bundle size, and aligns with the modern web platform. Native DOM APIs and polyfills now cover most common needs.

Bundler 2 needs Ruby 2.3.0+ and RubyGems 2.5.0+; older Ruby versions require installing the last Bundler 1 release with gem install bundler -v '~>1'.

AngularJS elements can flash visible before bindings apply. ng-cloak hides content until Angular loads; preadding ng-hide also prevents flicker but relies on internals.

Built-in CarrierWave image resizing helpers preserve aspect ratio, crop, or pad images to target dimensions, with MiniMagick and RMagick offering the same methods.

PostgreSQL fulltext search misses partial matches in dates, serial numbers, and other token fragments. Trigram indexes speed up wildcard LIKE searches on large tables.

Removing every table while keeping the PostgreSQL database can be done by dropping the schema or iterating through tables with DROP TABLE statements.

bundle install fails with Gem::GemNotFoundException when Bundler 2 runs on RubyGems 2; updating RubyGems to 3.0+ restores the bundle executable.

Uncountable Rails resources break normal route helpers and form handling. resource can still expose the index action through a special _index_path helper.

Basic Auth sends credentials as a Base64-encoded username:password string in the Authorization header; Ruby can generate it with Base64.strict_encode64.

Ruby can read and write CSV files with the standard CSV library, and smarter_csv makes imports more convenient when converting rows into hashes.

System-specific font fallbacks can make text look different across machines; Chrome DevTools can reveal the actual rendered font in the Computed panel.