Feature summary (what you would like to be able to do and where):
Document the "source:true" functionality, to use in MediaWiki:Visualeditor-quick-access-characters.json

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
User story: In order to make the interface of the 2017 Wikitext Editor more useful for other users, I as an administrator would like to know that I am able to mark an character on MediaWiki:Visualeditor-quick-access-characters.json with "source:true" to set it as only available in the 2017 Wikitext editor. An code example would be appreaciated.

After that an admin makes an wikicode available like this, an user can open up the special characters in 2017 Wikitext Editor and be able to use wikicode not present in VisualEditor.

Benefits (why should this be implemented?):
All WMF communities have a frequently added wikicode that gets added to multiple pages. The aim is to document that administrators can add an wikicode to MediaWiki:Visualeditor-quick-access-characters.json for their communities to use in the 2017 Wikicode editor only. This can reduce the editing time of the community and make them more productive.