Now this isn't just another What's the difference question, I have done some tests(http://jsfiddle.net/ZC3Lf/) modifying the prop and attr of <form action="/test/"></form>​ with the output being:

1) prop Modification test
Prop: http://fiddle.jshell.net/test/1
Attr: http://fiddle.jshell.net/test/1

2) Attr Modification test
Prop: http://fiddle.jshell.net/test/1
Attr: /test/1

3) Attr then Prop Modification test
Prop: http://fiddle.jshell.net/test/11
Attr: http://fiddle.jshell.net/test/11

4) Prop then Attr Modification test
Prop: http://fiddle.jshell.net/test/11
Attr: http://fiddle.jshell.net/test/11

Now I am confused about a couple of things, as far as my knowledge goes:
Prop: The value in its current state after any modifications via JavaScript
Attr: The value as it was defined in the html on page load.

Now if this is correct,

• Why does modifying the prop seem to make the action fully qualified, and conversely why does modifying the attribute not?
• Why does modifying the prop in 1) modify the attribute, that one makes no sense to me?
• Why does modifying the attr in 2) modify the property, are they meant to be linked that way?

Test Code

HTML

JavaScript

var element = $('form');
var property = 'action';

/*You should not need to modify below this line */

var body = $('body');
var original = element.attr(property);

body.append('<h1>Prop Modification test</h1>');
element.prop(property, element.prop(property) + 1);

body.append('Prop: '+element.prop(property)+'<br />');
body.append('Attr: '+element.attr(property)+'<hr />');

//reset
element.prop(property, original);
element.attr(property, original);

body.append('<h1>Attr Modification test</h1>');
element.attr(property, element.attr(property) + 1);

body.append('Prop: '+element.prop(property)+'<br />');
body.append('Attr: '+element.attr(property)+'<hr />');

//reset
element.prop(property, original);
element.attr(property, original);

body.append('<h1>Attr then Prop Modification test</h1>');
element.attr(property, element.attr(property) + 1);
element.prop(property, element.prop(property) + 1);

body.append('Prop: '+element.prop(property)+'<br />');
body.append('Attr: '+element.attr(property)+'<hr />');

//reset
element.prop(property, original);
element.attr(property, original);

body.append('<h1>Prop then Attr Modification test</h1>');
element.prop(property, element.prop(property) + 1);
element.attr(property, element.attr(property) + 1);

body.append('Prop: '+element.prop(property)+'<br />');
body.append('Attr: '+element.attr(property)+'<hr />');