chef

https://github.com/opscode/chef

Ruby

A systems integration framework, built to bring the benefits of configuration management to your entire infrastructure.

Chef::Resource.custom_resource?

Returns true or false based on if the resource is a custom resource.  The
top-level Chef::Resource is not a chef resource.  This value is inherited.

Source | Google | Stack overflow

Edit

git clone [email protected]:opscode/chef.git
cd chef
open lib/chef/resource.rb

Contribute

# Make a new branch
git checkout -b -your-name--update-docs-Chef--Resource-custom_resource--for-pr

# Commit to git
git add lib/chef/resource.rbgit commit -m "better docs for Chef::Resource.custom_resource?"

# Open pull request
gem install hub # on a mac you can `brew install hub`
hub fork
git push <your name> -your-name--update-docs-Chef--Resource-custom_resource--for-pr
hub pull-request

# Celebrate!