[jQuery] what's wrong with $(":checkbox[checked=true]") ?

[jQuery] what's wrong with $(":checkbox[checked=true]") ?


Hi,
I was trying to select for checked checkboxes so I tried
$(":checkbox[checked=true]")
this never returns anything, even though if I select all checkboxes I
can test "this.checked" for each one and it returns true/false as
appropriate.
I now understand that I can to :checkbox:checked, but I don't
understand why my original approach doesn't work, since clearly each
checkbox has an attribute 'checked' which has the value true or false.
Andy