Hello, my fellow geeks. I've stumbled upon something strange.

Steps to repro:

Have a display:none on body, check the value of $.support.shrinkWrapBlocks.

jsFiddle: http://jsfiddle.net/VWRzX/

Result:

$.support.shrinkWrapBlocks is true.

Occurs in Chrome 30, IE 10, Safari 5.1.7. Does not occur in Firefox.

Versions:

1.9.1, 1.10.1 (didn't try any older, 2.0+ doesn't seem to have $.support)

Cause:

This is the jQuery logic for shrinkWrapBlocks:

support.shrinkWrapBlocks = ( div.offsetWidth !== 3 );

Chrome, Safari and IE have div.offsetWidth = 0 when the div's parent has display:none.

Is this behavior a bug? It seems pretty wierd to me, I can understand offsetWidth being 0 when the parent is not visible, but having $.support.shrinkWrapBlocks = true makes no sense. The comment in jQuery code suggests that this property should only be set in IE6. Furthermore, it is counterintuitive that a field in $.support should depend on the document structure, I thought that $.support should reflect the browser's capabilities only.

One may argue that $.support is not a public API and should not be relied upon, but this causes other, public APIs to break. In our case it broke an animation that displayed a piece of our page (jQuery set overflow:hidden on something - if it is relevant, check out the defaultPrefilter jQuery method and the only usage of shrinkWrapBlocks therein).

This kinda thing can happen quite easily and, as you can imagine, can be tough to debug.