How to integrate custom language in the Code Search

[RobertvanderHulst]

We have created support for a custom language,
We cannot find documentation about what we have to integrate our language elements in the Code Search window.
Files are found, but we would also like to be able to support finding types and members.
Any hint would be welcome.
I have looked at the language service in the Roslyn repo, but there is so much code in there, that it is difficult to find which part of the code is reponsible for the Code Search