Can the compiler report errors by unknown attributes? Even with an eye?

Question

In N3291, "7.6.1. (3/5) Attribute Syntax and Semantics [decl.attr.grammar]" regarding how attributes are written in source code, I read

The use of the token-token-attribute is conditionally supported, with behavior defined by the implementation.

and

For a token attribute not specified in this International Standard, the behavior is determined by the implementation.

Does this mean that attribute characteristics such as

[[ dllexport ]]
[[ hiding ]]
[[ unused ]]
[[ vendor::attrib ]]

a complaint may arise with the standard appropriate compiler? So, can report an error and stop compiling?

, , , . , , , [[ noretrun ]] [[ carrys_dependencie ]]: -)

, ? [[ gcc::mips ]] Microsoft, , , ?

Answer 1

; " ".

, . . .

. , - , .

Answer 2

[[ vendor::attrib ]]

?

, , ( ).

. :

... -spec-fi-seq, , , ....

, , , , , , (.. , ), , . , , , .

gcc , , .