As it says here: https://github.com/leanprover/doc-gen4/blob/1e4a5c34bfa5e44ab37dd64de635db59572f627b/DocGen4/Load.lean#L29-L30
As it says here:
doc-gen4/DocGen4/Load.lean
Lines 29 to 30 in 1e4a5c3