wrapInner(function) does not have the same effect on an element as wrapInner(html), etc. Each of the first-child elements - including textnodess - gets wrapped individually, rather than, as intended, wrapping the contents into a single element.

As, wrapInner is a shortcut to $(elem).contents().wrapAll(fn), the contents get wrapped, one-by-one, by the beginning of $.fn.wrapAll(); This leads to the wrapInner(fn) callback being executed once for every child element, with the child element as 'this'.

http://jsfiddle.net/ZtBZ2/

<h3>foo<span>bar</span><div>baz</div>bam</h3>

<br/>

<h3>foo<span>bar</span><div>baz</div>bam</h3>

$("h3:first").wrapInner(function(i) {

console.log(this);

return "<strong style='display:block;border:1px solid #000'/>";

});

$("h3:eq(1)").wrapInner("<strong style='display:block;border:1px solid #000'/>");