I run a small web crawler and had to decide on what user agent to use for it.  Lists of crawler agents as well as Wikipedia suggest the following format: examplebot/1.2 (+http://www.example.com/bot.html)However some bots omit the plus sign in front of the URL.  And I wonder what it means in the first place, but couldn't find any explanation.  RFC 2616 considers everything in parenthesis a comment and doesn't restrict its format.  Yet it is common for browsers to have a semicolon-separated list of tokens in the comment that advertise the version and capabilities of the browser.  I don't think this is standardized in any way other than most browsers formatting it similarly.  And I couldn't find anything concerning URLs in the comment.My question is: Why the plus sign?  Do I need it?
Plus sign in front of URLs in user agents
web crawlers;http;user agent