[basic.splice]

The constant-expression of a splice-specifier shall be a converted constant expression of type std::meta::info ([expr.const]).

A splice-specifier whose converted constant-expression represents a construct X is said to designate either

(1.1)
the underlying entity of X if X is an entity ([basic.pre]), or
(1.2)
X otherwise.

[Note 1:

A splice-specifier is dependent if the converted constant-expression is value-dependent ([temp.dep.splice]).

— end note]

A non-dependent splice-specifier of a splice-specialization-specifier shall designate a template.

[Note 2:

A < following a splice-specifier is interpreted as the delimiter of a template-argument-list when the splice-specifier is preceded by the keyword template or the keyword typename, or when it appears in a type-only context ([temp.names]).

[Example 1: constexpr int v = 1; template<int V> struct TCls { static constexpr int s = V + 1; }; using alias = [:^TCls:]<([:^v:])>; / OK, a splice-specialization-specifier with a parenthesized splice-expression as a template argument static_assert(alias::s == 2); auto o1 = [:^TCls:]<([:^v:])>(); / error: < means less than auto o2 = typename [:^TCls:]<([:^v:])>(); / OK, o2 is an object of type TCls<1> consteval int bad_splice(std::meta::info v) { return [:v:]; / error: v is not constant } — end example]

— end note]

6 Basics [basic]

6.6 Splice specifiers [basic.splice]