API search inside a project or repo?

I’m looking for an endpoint to search inside a project or a repos, with a string parameter
it’ll search inside the content of the files
similar to the gitlab search bar , but using the api , if a project is given as parameter then the search isn’t global
something projects/901/search/somethingImLookingfor
I’m looking for it since 2days in the docs , and it’s not so obvious to find ? did I just miss something with my bad glassed eyes, does it exist ?
This is the project (documentation) I need to search in Pixel Humain / codoc · GitLab

suprised to find no answer to something I found quite essentiel
is my question unclear ?