Add rexml Is A Bundled Gem As Of Ruby 3.0.0 as a ruby til

ruby/rexml-is-a-bundled-gem-as-of-ruby-3-0-0.md

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+# rexml Is A Bundled Gem As Of Ruby 3.0.0
+
+Are you seeing an error loading certain
+[`rexml`](https://github.com/ruby/rexml) files?
+
+```
+LoadError: cannot load such file -- rexml/document
+```
+
+It may be that `rexml` no longer ships as part of the Ruby version you are
+using. If you are working with Ruby 3.0.0 or later, the `rexml` gem needs to be
+explicitly installed as it is now a bundled gem.
+
+Either add it to your `Gemfile`:
+
+```
+gem 'rexml'
+```
+
+or install it manually with:
+
+```bash
+$ gem install rexml
+```
+
+[source](https://stackoverflow.com/questions/65479863/rails-6-1-what-is-preventing-tests-from-running)