This is the HTTP standard way of giving a header multiple values. The response header is added to the existing set of headers, even if this header already exists. The response header of this name is removed, if it exists. If there are multiple headers of the same name, only the first one set will be removed. This argument is followed by a header name, which can include the final colon, but it is not required.
Case is ignored.
For add, append and set a value is given as the third argument. If this value contains spaces, it should be surrounded by double quotes. For unset, no value should be given. Order of Processing The Header directive can occur almost anywhere within the server configuration. This way round, the Author header is not set.