web idl 笔记

1、The type of the attribute is given by the type (matching Type) that appears after the attribute keyword. If the Type is an identifier or an identifier followed by ?, then the identifier must identify an interface, enumeration, callback function or typedef.

  大致意思是如果：如果类型是一个标识符或者标识符后跟了？，那这个标识符必须是interface, enumeration, callback function 或者 typedef

2、The return type of the operation is given by the type (matching ReturnType) that appears before the operation’s optional identifier. A return type of void indicates that the operation returns no value. If the return type is an identifier followed by ?, then the identifier must identify an interface, dictionary, enumeration,callback function or typedef.

  大意：如果返回类型是一个标识符后跟？，那么这个标识符必须是个interface, dictionary, enumeration,callback function 或 typedef