In your topics switches at Admin -> Settings -> Switches you have an "RSS Submissions" option. When you turn this on people will have the option to supply an RSS feed url with their submission. If they do, data from that feed will become available for the topic. Note: associated feeds properly defined in the html are automatically detected without the need for the submitter to type them in, so just the main website url will often work. Please note this associates with a particular topic, unlike the XML submission option which adds topics from a feed into a specified forum.
By default the data will be displayed in the topic details template, but you can put it anywhere. Use <!-- BEGIN FEEDS --> and <!-- END FEEDS --> to denote where the feed entry begins and ends, anywhere within the scope of a link. Then use {FEED + capitalized name of RSS field + } to display field data. For example:
<!-- BEGIN FEEDS -->
<a href="{FEEDLINK}">{FEEDTITLE}</a> by {FEEDAUTHOR} on {FEEDPUBDATE}:
<br>{FEEDDESCRIPTION}
<br>
<!-- END FEEDS -->
<a href="{FEEDLINK}">{FEEDTITLE}</a> by {FEEDAUTHOR} on {FEEDPUBDATE}:
<br>{FEEDDESCRIPTION}
<br>
<!-- END FEEDS -->
This is essentially what's in your topic details template already in WSN 8 and older -- or at Admin -> Topics -> Topic Fields -> RSS Feed -> custom display html in WSN 9 and later.
To control the number of feed items shown, insert the desired number between BEGIN and FEED: <!-- BEGIN 5 FEEDS -->.
The feeds are cached for 12 hours by default, you can change the cache timeout at Admin -> Topics -> Topic Settings. In the event of a bottleneck each page load will only update 3 caches, the rest will be left for the next page in order to not drag out page load time too long.
To detect if the feed is empty, use {LINKTOTALINFEED} in a conditional like <IF not {LINKTOTALINFEED}>No items in this feed.</IF>
Advanced Tasks
To get the attribute values of a self-closing tag, use {FEED + FIELDNAME + ATTRIBUTE NAME + }. For example, in podcast feeds there's often a line like this:
<enclosure url="http://..." type="audio/mpeg" length="1930012" >
To display the details of that referenced audio file, use this template code:
<a href="{FEEDENCLOSUREURL}">Download the {FEEDENCLOSURETYPE} file ({FEEDENCLOSURELENGTH} bytes)</a>
If you want to display the length in megabytes instead of bytes you can use some simple template PHP:
<a href="{FEEDENCLOSUREURL}">Download the {FEEDENCLOSURETYPE} file (<?php echo round(({FEEDENCLOSURELENGTH}/1048576), 2); ?> megabytes)</a>