[cpp.concat] p3 Is a placemarker preprocessing token considered as a valid preporcessing token

[cpp.concat] p3 says

If the result is not a valid preprocessing token, the behavior is undefined.

#define concat(X,Y) X##Y
concat(,)   // #1

The result of concat(,) is a single placemarker preprocessing token(result from the concatenation of two placemarker preprocessing tokens).

[lex.pptoken] specifies all normative preprocessing tokens, which does not mention placemarker preprocessing token. The note also says that:

Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that exist only within translation phase 4.

It is unclear whether the "valid preprocessing token" refers to the preprocessing tokens defined in [lex.pptoken] or refers to the tokens in [lex.pptoken] and the placemarker preprocessing token. Presumably, it refers to the latter. Furhtermore, the text "preprocessing token" in [cpp] intends to include the syntax preprocessing tokens and the placemarker preprocessing token.

[cpp.concat] p3 may be clearer if it is changed to

If the result is not a valid preprocessing token(include placemarker preprocessing token), the behavior is undefined.

Start by reading [cpp.concat] p3 alongside [lex.pptoken] and its note on placemarker preprocessing tokens. Check whether the standard consistently uses “preprocessing token” to include placemarkers, then determine wording that resolves the ambiguity. Done means an agreed clarification in the relevant standard-draft text.