The tracking issue for this feature is: #44027
doc_masked feature allows a crate to exclude types from a given crate from appearing in lists
of trait implementations. The specifics of the feature are as follows:
When rustdoc encounters an
extern cratestatement annotated with a
#[doc(masked)]attribute, it marks the crate as being masked.
When listing traits a given type implements, rustdoc ensures that traits from masked crates are not emitted into the documentation.
When listing types that implement a given trait, rustdoc ensures that types from masked crates are not emitted into the documentation.
This feature was introduced in PR #44026 to ensure that compiler-internal and implementation-specific types and traits were not included in the standard library's documentation. Such types would introduce broken links into the documentation.