The spec indicates to use @@ to delimit multi-line tags.  Other popular languages however support multiline tags without needing special delimiters (e.g., both JavaDoc and JSDoc).

To align better with other implementations, consider changing:

The contents of the resulting tag will be whatever comes after the tag definition until the end of the line, or the comment-block, whatever comes first.

to

The contents of the resulting tag will be whatever comes after the tag definition until the next tag or the end of the comment-block, whatever comes first.

This forces the author to put all tags at the end of the comment block, but I think that's fair and matches how tags are usually used.  If you really wanted to support non-tagged comments at the end of the block, you could further update the description such that the tag content also stops if there is a blank line.