[basic.scope.param]

[Note 1:

A function parameter cannot be used for its value within the parameter-declaration-clause ([dcl.fct.default]).

— end note]

(1.1)
If P is associated with a declarator and is preceded by a (possibly-parenthesized) noptr-declarator of the form declarator-id attribute-specifier-seq $_{o p t}$ , its scope extends to the end of the nearest enclosing init-declarator, member-declarator, declarator of a parameter-declaration or a nodeclspec-function-declaration, or function-definition, but does not include the locus of the associated declarator.

[Note 2:
In this case, P declares the parameters of a function (or a function or template parameter declared with function type).

A member function's parameter scope is nested within its class's scope.
— end note]
(1.2)
If P is associated with a lambda-declarator, its scope extends to the end of the compound-statement in the lambda-expression.
(1.3)
If P is associated with a requirement-parameter-list, its scope extends to the end of the requirement-body of the requires-expression.
(1.4)
If P is associated with a deduction-guide, its scope extends to the end of the deduction-guide.

6 Basics [basic]