Most web rings have "rules" for admission into the ring, for being added to the ring, and for being kept in the ring.
what are the ring rules?
The ring rules dictate who can join the ring and other requirements for addition. These generally have to do with what type of content can or cannot be on your site; where you have to keep the fragment; and the procedure for getting your site added to the ring.
what are the most common rules?
Rules for admission are generally things like: "your page must have something to do with widgets;" "you must put the ring fragment on the page having content to do with widgets;" your site cannot have any nudity or links to nudity;" and "you cannot link to the ring image on my server."
Then there might be some rules for getting your site added to the ring, like: "you must have the ring fragment on the page you registered with the ring;" "you must have the code published within 10 days of submitting your site to the ring;" "you must e-mail the owner when you have published the code."
Finally, there might be some rules for staying in the ring, like: "you must keep your site information registered with the ring current;" "you must continue to keep the ring on a page with information about widgets."
why are the rules important?
It's fairly important you understand the rules when applying to a web ring, if you don't then you're wasting both yours and the owner's time. You'd be amazed at how many people join rings and obviously haven't read the rules.
Other common rules are those against pages with hateful or racially degrading content; those with information or links to information that are illegal like hacking or warez; pages that infringe on the intellectual property rights of others such as copyrights and trademarks.
These types of rules become especially important if you're trying to keep the ring "family friendly" and "politically correct."
finally. . .
Many owners are very particular about who they let in their ring and others just want as many people to join as possible.
Some rings you can't join at all, they're by invitation only, or maybe you can submit your site, but you're not allowed to add the ring fragment until you've been approved.
Every ring is different which is just one more reason why they're so great!