HTML has two link relationship attributes, rel and
rev, which apply to the link and
a elements. What values are most used?
Methodology: The analysis counted separate keywords in
the same attribute as separate keywords, so for example
rel="a b" counted as one a keyword and
one b keyword; with one exception: if
alternate and stylesheet were
specified on the same link element's rel
attribute, then that was counted as one stylesheet
alternate keyword instead.
From these results we can see that the most common relationship
by far is <link rel="stylesheet">, which isn't
surprising, but we can also see that the second most common link is
the one that gives custom favicons for the page
(rel="SHORTCUT ICON" to be compatible with IE, or just
rel="icon" if it is only intended to work on the other
browsers — hence the two values in the results, and hence
the slight difference in frequency). In other words, the two most
common link relationships (by far!) are presentational.
The rel="alternate" value is mostly RSS feeds,
rel="edituri" is a blogging autodiscovery value, and
the rel="service.post" value that barely scrapes into
the top 20 is part of the Atom API. We can therefore determine that
blogs are not a negligible part of the Web these days (and that
Atom is reaching relatively wide deployment, given that it is still
a young technology).
An interesting thing to note from this is that the only
<a rel=""> value to appear on the list of the top
20 relationships is Google's rel="nofollow", and the
only <link rev=""> link to appear is
rev="made" (to point to the author's page) —
and the latter is not used that much more than the more sensible
rel="author". Also, ironically, just off the graph in
position 21 is rel="made", probably showing that the
distinction between rel and rev may be
too subtle for many authors. More evidence of this is at position
29 on the list, with <link rev="stylesheet">. The
first <a rev="">, rev="made">, appears
on the list at position 96, beyond the point of statistical
clarity.
The rel="file-list" value
is part of Microsoft Office's HTML output.
Alternate stylesheets (which were specifically counted
separately — the rel="stylesheet" and
rel="alternate" entries don't include
rel="alternate stylesheet" entries) are, surprisingly,
in the top 20 (barely). They don't seem that popular, though,
relative to normal stylesheets.
Not shown above, but 33rd on the list, is
rel="pingback", of the Pingback
Specification, written in 2002. Around the same time, Tantek
Çelik was recommending that people use <a
rel="bookmark"> for permalinks; they come in at number
39. (Oddly, <link rel="bookmark"> is used more,
coming in 34th on the list.)