Hi,
In a recent investigation into capacity issues, I found that there are several instances where the browser will make a second to the page based on resolving empty-string URLs in the several tags. I tested four instances: <img src="">, <link href="">, <script src="">, and <iframe src="">. Across major browsers today, the behavior is vastly different: * Internet Explorer 8 - Make a request for: <img src=""> - Does not make a request for: <link href="">, <script src="">, <iframe src=""> * Firefox 3 - Make a request for: <img src="">, <link href="">, <script src=""> - Does not make a request for: < <iframe src="">. * Firefox 3.5 - Make a request for: <link href="">, <script src=""> - Does not make a request for: <img src="">, <iframe src=""> * Safari 4 - Make a request for:<img src="">, <link href="">, <script src=""> - Does not make a request for: <iframe src=""> * Chrome 3 (same as Safari) - Make a request for:<img src="">, <link href="">, <script src=""> - Does not make a request for: <iframe src=""> * Opera 10 - Make a request for: (none) - Does not make a request for: <img src="">, <link href="">, <script src="">, <iframe src=""> Presently, HTML5 does provide guidance on the correct behavior for <img src=""> in section 4.8.2, indicating that Firefox 3.5's and Opera 10's behavior in this regard is correct: "If the base URI of the element is the same as the document's address, then the src attribute's value must not be the empty string." This seems like it should also apply to the other elements that download resources automatically. All browsers seem to be in agreement over the behavior of <iframe src=""> despite a lack of guidance in any HTML spec, and I'd assume that they will soon all be in agreement over <img src="">, per the HTML5 spec. It would be nice to formalize this behavior so that we can get all browsers to act in consistently in these confusing cases. My opinion is that Opera is the only browser currently doing this in a reasonable manner, in that it makes a lot of sense to me that an empty-string URL for an element that automatically downloads a resource should be considered invalid and ignored. My hypothesis is that these patterns are most frequently indications of errors rather than an intentional use of this little-known behavior, and as a result, sending another request is an unexpected and unwelcome result. For high-volume web sites, a single mistaken inclusion of one of these patterns immediately doubles page views, which can introduce capacity issues (which I've needed to investigate at least twice in the past three years). I'm interested in what others' opinions on this may be, as this seems like an important area in which to gain consistency. -Nicholas ______________________________________________ Commander Lock: "Damnit Morpheus, not everyone believes what you believe!" Morpheus: "My beliefs do not require them to."