I am trying to find samples or code which help me to build a provider of insert-stuff elements: in the list of Insert Stuff sources, for desire to learn for my custom service.
Example Same as the option of youtube in insert on html editor
Any pointers or guidance will be appreciated.
Have you checked out the Remote Plugin Test Service sample? There's a blog post about the sample in the Dev CoP blog (https://community.brightspace.com/devcop/blog/making_development_easier_with_the_remote_plugins_test_service~1) and the sample includes an Insert Stuff Remote Plugin.