@used-by

The @used-by tag documents that the described element is depended upon by the referenced one — the inverse of @uses. Where @see simply says "read also", @uses/@used-by express an actual dependency worth tracking: if a change to this element could break the referenced one, @used-by is how that relationship is written down. The two tags are typically used in pairs — if A is annotated @uses B, B is often annotated back with @used-by A — so the dependency is discoverable by reading either side.

"@used-by" <Reference> [ <Description> ]

Parsing a @used-by tag produces a ReferenceTag instance narrowed to a CodeReference (a class, function, method, constant, property, or variable — never an external URI), exposing $reference.

final class UsedByTag extends ReferenceTag
{
    // extends ReferenceTag<CodeReference>
    // directly; adds nothing beyond the
    // inherited $reference, $name and
    // $description.
}

Defined by phpDocumentor, alongside its counterpart @uses.

05 July 2026