Suppose I have two links on my webpage as:
<a href="/balls" rel="tag">The Balls page</a>
<a href="/bats">The Bats page</a>
Would browsers or crawlers deal these differently?
The rel attributes are SEO elements that, when used properly, can help you provide important information to search engine crawlers. Unfortunately, rel attributes are often unused in full potential, which leads to missed opportunities in terms of taking control of a site’s pages.
The basic nature of the rel attributes is that they are components of HTML that describe a relationship between pages of a site. These components affect the site’s linking structure. Because links are a huge contributing factor to search engine algorithms, taking advantage of rel attributes will only help one’s ranking potential.
The rel attributes are placed at the back-end of given site, attached to the links they are providing "instructions" for. That way, when search engines crawl the site, they are able to identify your intentions regarding particular links.
In the case when the anchor tag (<a>) has rel attribute, the rel attribute specifies the relationship between the current document and the linked document. They are only used if the href attribute is present. The rel attribute is simply a tag (keyword) for the current document.